I find the "Life isn't fair" aphorism to be glib and annoying. It strikes me as an excuse people use to justify bad behavior (like promoting toxic mortgage-backed securities, for example).
However, I've found that I can block the aphorism by saying, "Thus-and-such isn't RIGHT" or "Thus-and-such is WRONG." In my experience, most people who are willing to smugly tell me that life isn't fair are less enthusiastic about condoning practices that are demonstrably wrong (like promoting toxic mortgage-backed securities, for example).
In the OP's situation where lots of kids are bending rules, I would probably try to encourage seeing the big picture. For example, when I'm in a similar situation, I tell myself or one of my kids, "Yes, these people aren't following the rules precisely. However, there are also times when I/you don't follow the rules precisely [example, example]. Sometimes people use their judgment. You may not agree with what that person is doing, but you do have to admit that you do the same thing. And other people might not agree with your decision."
So the question becomes, "When can 'wrong' actions be overlooked and when is it time to speak up?" Of course, this is a tough question to answer, but I think it gives a thoughtful child (or adult, in my case) something to think about. And it also encourages the person to think about his or her own rule-bending decisions.
