It's crazy how many people don't seem to understand the part of the intro that says "To be a man in such times is to be one amongst untold billions. It is to live in the cruelest and most bloody regime imaginable." It's pretty unambiguous. Hell in some of the lore there are plenty of places that actually seem almost pleasant to live in, though they rarely last long without being imperial or disappearing.

The Imperium isn't even the good guys to humans lmao

corpse starch sounds like a conspiracy theory some rightoid in the boonies thinks is going on at McDonalds

As someone who isn't a fan of Guilliman coming back and actually being a noble ruler (as opposed to previously the super sketchy high lords, who I thought fit a grim dark degraded tone much more), I've always considered 40k to be the bad ending. If there was a video game, the 40k we know would be an ending slide that happened when the player had truly made terrible choices. The game is over and we are stuck in the bad outcome. It won't get better.

Humanity in 40k is collectively a corpse that doesn't know or accept that it's already dead (just like the emperor himself- symbolism!). The most humanity can do are have brief moments of staving of things getting worse. Humanity can at massive cost and misery preserve a terrible status quo every now and then and call it a victory, but even the victories just lead to losses and the losses keep leading to the final death of humanity.

Justified in universe, possibly. Good? No, they're fucking evil on a good day. But that's the point. Sure they're evil, but are they the most evil? No. The entire 40K universe runs on Gray and black morality; there's no such thing as good there.