If someone was an asshole, but has decided to stop being an asshole and try out "being a nice person" instead — then your choice, as an onlooker, is between either encouraging them in their new take on life; or pushing back due to their past actions. Through your actions, you can choose to live in a society where "turning over a new leaf" like that is either incentivized, such that more assholes become not-assholes... or disincentivized, such that the assholes' takeaway will be "damned if you do, damned if you don't", and they'll likely not bother, and keep being assholes.
Clearly, one of those options is better for the public good than the other.