Not the kind of people an aspiring Emperor wants in his autocracy.
Free people with courage, honor and a desire to be free. No wonder the thing fell apart. Also I don't think the Imperium is autocratic, its more a cast based society, God King, gene enhanced super warriors, noble families, useful yet still powerless people to do the actual work and fighting, most of unwashed humanity to do the actual work, then slaves, mutants and lobotomy victims to do the even worse work, then your occasional person who thought of a different way that you burn at the stake and take everyone's mind away from the actual problems, all strangely like real life.
Everyone thinks the Horus Heresy changed things but all it did was put the noble families in charge rather than the space marines.
As far as evil it is definitely Papa Smurf. Not only for Virus bombing the Imperium and crippling it but the horrible hypocrisy he had. Doing this right after whining about how bad the World Eaters and Night Lords were, whining about courage and honor and then running away when the odds were against him. A war criminal weakling hypocrite.
Needless to say I was dissopointed when Honsou didn't defrost him show him then show him what a failure the Imperium had become and then use his skull as a drinking glass. Yea Games Work Shop HAD to have Honsou fail and could'nt allow something interesting to happen, sigh.