While I'm sure it gets you hurt quite a bit I'm not sure that there's really anything wrong with the way you see people.
I'm a cynic. I honestly don't see good in too many people, not without me knowing them really well. I have yet to meet anyone who wasn't completely out for themselves and present themselves to the world as something that they aren't. Fakes and phonies if you ask me... Maybe I'm missing out on some good people, maybe not.
Until I meet someone who is genuinely good, whos intentions are genuinely good, and that person does not exist (that's the cynic in me) I doubt my ability to trust in other people will ever change.
All I can say to you is, don't be as cynical as me..
but maybe just keep your eyes open to other people, and pay attention to them, and to your instincts about people, your instincts are rarely ever wrong. If something seems to good to be true, it is. Not saying to look for flaws in people, but maybe just take them at face value, and don't beleive everything you see.