If they get very small prize for socially accepted behaviour, they cannot think they did sth socially accepted for that prize - that would mean they are cheap to buy. So they think they did it because they are the kind of guys, that do such things sometimes.

If I'm doing small acts of kindnes just because, it's hard to make this consistent with "fuck the others" attitude, stealing, etc. Easier to think I'm good guy overall, just made some mistakes before. Cognitive dissonance is a powerfull force.

But IANAP.