This reminds me of a post I saw on Facebook: "I used to think I was in a bad mood, but it has been a couple of years now, so I guess this is just who I am now."
Anyway, I think an argument that defuses cynicism is this: (1) Cynicism is generally believing that everyone is bad and it doesn't even bother them. (2) But it bothers you. (3) So that's one person in the world who's not as bad as you bemoan. And it would be unreasonable to think that you are the only person like that.
That's an intellectual answer but not an emotional one, which is equally important, because cynicism I believe is an emotional adjustment. People keep disappointing you. That hurts. If you lower your expectations, then they won't disappoint you so much. Voila! Intermittent sharp pains are all replaced by a chronic, everpresent, dull one. Many people seem to prefer it this way. But obviously something inside you has died.
A fuller treatment requires me to talk about religion, which is frowned upon here. Suffice it to say that if you believe in the Fall then you see the current state of affairs just like someone who doesn't believe in the Fall. But your attitude about it is different. Your attitude is, it makes perfect sense why I'm discontent with the way things are.