Michael Caine would stand on a ridge of sand looking out at the ocean and shout 'Stop spraying. Bloody oil. At me.' and it would stop despite having overwhelming odds.

Surely the point is that the moral appoach taken by Kick Ass is completely at odds to that taken by Hit Girl and Big Daddy. He is doing it because he thinks super heroes should be out there helping people while they are doing it out of pure revenge and spite. That's shown pretty categorically right from their first meeting where KA is basically appauled at the willingness of HG to just kill everyone in the room, no matter their level of involvement.

If anything the problem should be with the ending where KA basically gives up his moral outlook after allowing himself to be emotionally blackmailed by HG.