I mean there is an argument, whether you agree with it or not, for moral relativism, and in that case I certainly would say that in-universe, a moral relativist would consider the imperium the good guys.
There is an argument, but I don’t think it’s convincing. The single best way to cripple their most deadly foe (so far) is to be less evil and make everyone’s lives less shit. They could hamstring chaos by simply ceasing their eternal crusade and focusing on improving the average peon’s life. The Imperium as a state only exists because of a “well-intentioned” checks notes… galactic crusade of conquest and omnicide against any non-human. In pretty much any other media they are unambiguously the bad guys, having other bad guys to fight doesn’t change that. They are literally a characture of every evil space empire. We just get fed so much propaganda that it starts to work a little.
