Ah, the Psychlos. The "oh God, is he really being that blatant with the allusion to psychology?" Psychlos. The scourge of worlds, the overlords of universes, the bad guys of Battlefield Earth. And there's so much stupid about them.
I've already covered their bizarre biology as it came up in the book, but let's recap. These things respire something called "breathe-gas," which as we learned reacts explosively to uranium - or possibly radiation, since the terms might be synonymous in Hubbard's mind. Their eyelids and lips are "eye-bones" and "mouth-bones" respectively, and it could be interpreted that their hair is bone as well. Their skull is in fact mostly bone, with the brain smushed down against the spine like an afterthought. Their heart lies low in the torso near the belt buckle, and there is no mention of a protective boney structure covering it. They have an extra finger on their right paws, bringing their grand total of claws to eleven, not counting toes. And, in one was probably meant to be a symbolic gesture but instead makes the author appear an absolute idiot, they are supposedly viruses which have managed to form cells, organs, and a method of sexual reproduction, all in utter defiance of the very definition of a virus.
They're twice our height and strong enough to carry a horse under each arm, which combined with all the bones and whatnot would make them a lethal enemy to face in combat. Except it doesn't. Jonnie mops the floor with them in hand-to-hand, and their spectacular weakness to radiation makes them explode from one irradiated bullet. Even with the Psychlos' advanced technology, the battles at the minesites or in Africa go overwhelmingly in the humans' favor with kill ratios of at least fifty to one. Their supposedly invincible war machines prove susceptible to centuries-old bazookas or getting flipped by a mortar.
The question with the Psychlos is not how a bunch of Air Force cadets in Colorado could hold out for hours against the invading aliens, but why the rest of the world's military did so poorly. Yes, there was a gas attack, but apparently nobody made it to the fallout shelters or had a gas mask handy or bothered to make a phone call to a neighboring country to warn them about the gas drone lumbering their way. And I'm just going to mention once how achingly stupid it is for the gas drone to fly through a nuke unharmed but have its door hinges blown off by weapons fire from Jonnie's fighter.
I think Hubbard was wanting us to be impressed that Jonnie and the other humans could succeed against such a strong and dangerous alien species, but the ease with which they do so really undermines their accomplishment. Downing a Psychlo is about as impressive as watching a Star Wars character cut down Stormtroopers or those stupid Battle Droids by the dozen.
But that's just one aspect of what's wrong with them.
Consider the Psychlo Empire. The Psychlo civilization, as mentioned before, has a mining fetish. Cities are built like minesites. Public transportation looks like minecarts. They invade planets to mine them for metals which they sell or process to finance the next invasion to acquire more metals. Their very numerals are based on mining. They have no art, no literature, just an interest in digging and smelting. The Psychlos are one-dimensional, and their choice of dimension is an odd one.
That's just the Psychlo culture, though; what's really stupid is how the Psychlo Empire operates. They've built it around their teleportation technology, which they rely on nearly to the exclusion of all other forms of interstellar transportation. This would make perfect sense, since after all instantaneous travel is preferable to spending months on a space ship, if it weren't for the limitations of teleportation - the key one being you can't teleport near a location already undergoing a teleport. Limit one per planet, in effect.
So knowing this, the Psychlos come up with a plan. They'll use their homeworld and capital of Psychlo as the hub for the empire's teleportation network. It will only run one teleport at a time, and to avoid mishap it will run on a strict schedule, with each world in its vast empire only having a few hours per year to make contact with the homeworld, to exchange news and material and personnel.
How the hell would that work?
It abides by Hubbard's baffling and plot-convenient rules for teleportation, but is woefully ignorant of the kind of infrastructure required to run an elementary school, to say nothing of a city government, nation, or heavens forbid an interdimensional empire. The Earth outpost has three hours or so to get a year's supply of food and breathe-gas transferred, while sending off a years' worth of mined ore and exchanging workers and correspondence. If some disaster strikes the colony's food supply and they run dangerously low, or sickness plagues the workers, or a rival alien race attacks, they get to wait a whole year until they can send a message for help. If someone like the Tolneps took over a Psychlo world, the first the Psychlo capital would know about it would be when a stack of rocks didn't appear on the teleportation platform as scheduled. What would they do then? Send an inspector, or a note asking questions, and expect an answer the following year?
And speaking of years, the Psychlo and Earth calenders conveniently match up. Which means that, assuming 365 days in a year and an approximately three-hour window to make contact, the Psychlo capital would only be able to link up with 2,920 of its 200,000 planets. So some worlds were out of contact for more than a year at a time. And, of course, this leaves no room for military campaigns.
Empires don't run that way. Especially supposedly paranoid and dictatorial empires like the Psychlos', who are worried about its secrets being stolen or its population getting out of control. This also makes Jonnie's worries about an imminent Psychlo counterattack extremely pointless. They'd only have one chance to do so, for a few hours, at a predictable time. If they're dumb enough to pop in on the platform, you could just irradiate it and watch them explode.
And then there are the catrists, those charlatan mind-doctors who secretly run Psychlo society, are responsible for all their evil, and we only learn about in the last couple of pages of Battlefield Earth, long after they're dead. I'll do the whole Scientology angle later (though not much needs to be said, really, Hubbard's not being subtle here). The main thing is: they wanted to implant a safeguard to preserve the secret of teleportation, check. And they wanted to program their population to be happy workers, check. But something went wrong with the wiring and it turned all the Psychlos evil. And they put in the implants anyway.
Why? Why don't you, I dunno, fix the design so it brings about the desired result? Even if the catrists were utter morons and did the implants to everyone without testing or a control group, why would you continue to use them on subsequent generations? And if you're restricting the secrets of teleportation to "trusted" and "brilliant" individuals like Terl anyway, do you really need to implant every single citizen?
The answer is obvious, as Hubbard meant it to be: the catrists are Pure Evil, malicious for the sake of malice, causing misery even without the promise of personal gain. They want their people to be bloodthirsty and stupidly aggressive, rather than placid and happy. I can only assume it fits in with the "we're all nothing but animals" philosophy Ker mentioned the catrists pushing - the catrists are simply using mind control to ensure that society lives down to their expectations. Sort of like altruists using mass hypnosis to force people to help each other and cooperate, or Flat-Earthists using a superweapon to reshape the Earth into a rectangle. Stupidity combined with supervillainy. Stupervillainy.
Except - and here's the biggest problem with the Psychlos, the one that makes the book fall apart - the Psychlos aren't all that evil. We're told that the implants make them bloodthirsty, and that they have an addiction to causing pain and suffering. There's that incident with the captive Scotsmen the Psychlos tortured to death (in the process of evacuating, because they are idiots), and the Scots relate how they can't raid close to the Psychlo base, lest they be captured. There's corporate screwing over, and that one Psychlo whose name I forget sabotaged Terl's demonstration for the lulz. And wives can be purchased, so they're misogynist too, though nice enough to let females work as secretaries.
And that's it. When we see the Psychlos at the mine site off-duty, they're getting drunk or playing ring toss. In the very first chapter Char wonders why anyone would go through the trouble of hunting humans. We don't see the Psychlos flying out to find the ragged remnants of humanity and strafe them from a plane - not on company time, they aren't! When we see the Psychlo workers, they're not wondering when they'll be able to rip something to shreds, they're worried about pay cuts and downsizing. None of the Psychlo captives make suicidal attacks on their captors to sate their bloodlust, or tear each other apart in a frenzy of aggression. We don't see gladiatorial arenas on the Psychlo homeworld, or hear of the slave ships crammed with helpless sentient creatures for the Psychlo population to torture to death in the privacy of their own homes. They're pretty normal for twelve foot, explosive behemoths.
And Jonnie kills them. By the dozen, personally, and by the billion, indirectly and a little accidentally. He kills miners defending themselves against a sudden attack by creatures they had never heard of, or didn't know were sentient. He kills unemployed Psychlos trying to make a living on their overcrowded and economically-stratified homeworld. He kills Psychlo females who live in a society where wives can be purchased. He kills Psychlo children who haven't been implanted with the catrists' control units yet. In Jonnie's effort to subject planet Psychlo's teleportation nexus to a dozen or so planet-buster nukes, he sets off a chain reaction that ends in genocide, with the only surviving Psychlos all sterile workers. And he is lauded for it.
This is a race supposedly under mind control, remember? An empire ruled by a shadowy oligarchy, right? But there is no lamenting that more Psychlos could be freed, or that Jonnie could have somehow defeated the catrists to liberate the aliens. Instead the Psychlo Empire is equivalent to the Psychlos as individuals - since they are part of the machine that invaded Jonnie's planet a thousand years ago, they are fair game. The Psychlo Empire invades planets, so the Psychlo species must die.
Tolkien struggled with this. His Orcs were brutal and nasty creatures that ended up treated, to drop a link to TV Tropes, as Always Chaotic Evil and therefore perfectly okay for the protagonists to kill. But this clashed with Tolkien's beliefs of goodness and redemption, and he could never really justify why it was okay to slaughter orcs by the hundreds. He did better with the human tribes who ended up allying with the bad guys, and explained that they were largely misguided or lured by false promises or simply bullied into compliance. There's a lovely bit where Sam (in the books, Faramir in the movies) looks upon a dead soldier and wonders if he was truly evil, and what drove him to march from his home to die in a strange land.
Jonnie doesn't wonder, and Hubbard doesn't struggle. He expects us to feel elated when we learn of the utter destruction of a species who had the misfortune of living under a dictatorship, as if anyone would break out the champagne if a meteorite flattened North Korea. To Hubbard, the Psychlos are pure evil worthy only of extermination and it doesn't seem to occur to him that anyone would think otherwise. And that's pretty frightening, especially if you read Battlefield Earth as a Scientologist statement.