I've heard people justify working there (often to themselves) by saying things like, "If I don't do it, someone else will. So, I may as well do it and make virtuous use of the money."

I think some people also tell themselves that they'll be agents of change and fix things from within but that almost always winds up being another self delusion at worst and impossibility at best. There was a certain amount of this on display in Careless People.