I just earned the "Cleanup" badge on Stack Overflow for rolling back my own edit.
Should I be able to earn a badge that way?
Sure, why not?
Badges are there for positive reinforcement, so rolling back a post should always be done with the motive to improve the site's overall content (more up-to-date, more accurate, etc.).
So it really doesn't matter which post you improved -- it's the act of improvement that's being rewarded.