I'm calling the Thought Police!
Most of the "alien" humans in the Marches are not particularly alien in that they're easy to understand from an early-21st century point of view...
Zhodani are weird. Ok, they're psychic space Soviet Socialists, but what does that mean? They don't think or act the way 21st century Westerners (or, really, anyone currently alive) would. They don't even think or act quite how you'd expect individuals with psionic abilities would, because in our present context they'd be isolated people with super powers rather than part of a culture built around and upon psionics.
I have to admit I was one of the few that voted for the Zhodani as my "favorite sophont in the Marches." Because they are written in, (what would become,) a classic GDW fashion. And frankly, they were my first experience with that style of writing.
First, I think it's important to remember that in the first edition of the little, black books, there really wasn't any mention of aliens. The rules were written around a human-centeric universe, with no thought of any sort about aliens. So, when GDW got around publishing their alien modules, the first few were about cat-people and dog-people. Science-fiction staples, I'm the first to grant. But hardly ground-breaking.
It seems it took several years of trial and error for GDW to stumble across, what I feel, is one of the most inspiring methods of writing about aliens.
Take one little thing, the smallest change from the human condition, and expand upon it to the nth degree.
Personally, I think this came to a pinnacle in
2300 AD, and the aliens therein. But you can certainly see it in the development of the Zhodani.
They asked a very simple question... "What if a significant number of people were psionic? How would this change society?"
Other science-fiction venues, particularly
Babylon 5, have expounded upon this question. But as far as I'm concerned,
Traveller was there first! (Well...right after Isaac Asimov.)
(Interestingly, I believe it's worth mentioning that, (if I understand correctly,) MWM has a degree in sociology.)
By following a thread that psionicly endowed people would use their abilities to control society, that led down to the logical conclusion the all of that society would be essentially brainwashed. The psionics would control the populace by "adjusting" any unwanted thoughts among that populace. And they'd be happy about it! Because, if not, you'd just "adjust" them until they were.
Brilliant!
And to my way of thinking, a little disturbing. Which made them the perfect "bad-guy" for the Imperium. After all, who would ever want someone to come in and, *poof*, suddenly you were not allowed your own thoughts and feelings? Those thoughts and feelings were now dictated by the state. I can certainly see why the Imperium would fight to the death, if needs be, to prevent that from happening.