how about 'the emperor shouldn't have created a galaxy-wide totalitarian meatgrinder that only serves to multiply human misery'?
"The Imperium is/was doing what has to be done" is the worst 40K take. It's literally buying into arguments that are presented satirically. No empire that fights wars with giant space cathedrals full of actual chain gangs hauling shells into place with actual chains is doing things sensibly or efficiently. No scaremongering about external threats makes sense if an empire then goes on to survive 10,000 years without the guy who claimed he was the only protection. Please don't read warhammer as pro-fascist.