A big word at the centre of many peoples belief system is "Fair." I should be treated equally, you need to play by the rules, life should be Fair. A thesaurus puts the word alongside Just, Honest, Trustworthy, Lawful, Legal, and Good.
The average person believes that fairness, or you could say justice, should be enforced in society. In a perfect world, the average person will be treated justly. The problem, however, is that when people think this, they have forgotten that the average person is not perfect. In fact, all of humanity is imperfect, and the familiar phrase "I'm only human" is one piece of evidence that shows we already know this. It's not news, but neither is it a welcome fact.
We are a broken species; we spend as many days behaving badly as we do behaving well, if not more. If you think this excludes you, then I'll add that even if you don't act on bad thoughts, all of your selfish and overly-proud thoughts are as valid for judegment as any actions. Your actions are, after all, only a symptom of the real character within you.