Don't forget that humanity turns into an exceedingly fascistic/fanatically religious and almost absurdly authoritarian dictatorship, with literal superhuman stormtroopers enforcing its might. Also cosmic horrors from beyond time and space, civilizations that literally feed on the souls of tortured prisoners, terrifying unfathomable alien hive minds and warmongering sentient fungus-grown brutes who irreversibly infest every world they touch.

Fun times.

Also originally a scathing commentary on Thatcherism and British society, similar to Judge Dredd, but that has been toned down a lot over the years, unfortunately.

That's it. I'm joining the T'au.

Or the fact that planetary genocides are de rigueur in that universe.

Well, in their defense, the planetary genocide is partially justified. When do they call it: - Ork infestation. Without scorching most of the air and ground, Ork spores will just give bigger nastier Orks, and a possible staging ground for further infestation. - Tyranids. Yeah, you're just doing whatever Tyranids would do anyway. Plus denying them resources - Chaos. Even if there is a single heretic, they can spread their belief around and then use psykers to turn the planet into a Warp world, which is a fate worse than a virus bombing.

(I do know there have been a Tau and Necron Exterminatus, but I did said partially justified)

It's funny. In Warhammer 40k lore, any society that didn't practice witch burning was essentially wiped out by daemonic incursion. Therefore Warhammer 40k human world evolved to a racist, xenophobic, psyker-hating society.

Fair, still a shit place to live in though. Even if killing your planet is justified, you’d rather not be there for it.