If the crowd in the movie cheered when Rogen's character shot a flasher, then it seems to me that it was entertaining the larger part of the audience. Comedy=happy ending. For what it's worth, I don't think I would have been entertained either.
The words "redeemable" and "consequences" are confusing me. Comedy is about conflict and the resolution of the comedy is about the happy ending to the conflict. If the mall cop was irredeemable then there should have been no happy ending. And killing the mall cop would have still have allowed the audience to enjoy all the shenanigans up til the formal concession that the protagonist was a prick.
It is possible for a comedy's happy ending to be a just reconciliation of the parties, with redemption for all. In farces, the conflict is free from serious consequences; in tragicomedies, the conflicts end with realistic consequences. In other comedies, the plot carefully contrives to limit the consequences to the conflict, and devises a plausible reconciliation (including redemption as needed) if possible. Many comedies just end in a welter of absurdities and sentimentalities of course. It sounds to me that Observe and Report is just another comedy where we're supposed to identify with the lead doing the things "we" are supposed to want to do (on some level, not in cold blooded reality, of course.) It all hinges on whether we identify with the Rogen character. It seems unlikely I would.