It's been repeatedly implied that Palpatine has no qualms about doing dirty work for Plagueis, and that he has no problems with all the stuff he's done. Yet how come in the end in his breakdown, he begins to relive and enumerates all the stuff he's been forced to do like he hates it?
Palpatine probably just hates being a servant to anyone.
This most likely. He'll murder puppies for gits and shiggles, but if someone tells him to do it, he'll probably bristle at it even if he was going to do it anyway.
He as much as says this, berating Plagueis for trying to turn him into "a mere messenger and intermediary" and saying that he's grateful to Plagueis as a teacher, but never as a Master.