Also it's ostensibly somewhat rational in the lore, at least compared to lots of the Imperium's nonsense. Without doing it interstellar travel becomes impossible, and the people they're throwing into the fire would have been euthanized anyway since they randomly turn into satan portals if they can't handle their shit.

40K's satire mostly isn't only actually about exaggerating the size or nature of atrocities (not that it doesn't do that), it's often in demonstrating how utterly batshit the universe would have to be for things like that to be halfway rational.