I've been there. It's hard. Please continue to be idealistic about the potential of people. Balancing hope against grounded expectations is a worthy goal though.

If you (not you specifically) already believe that you are a good person, will you continue to work to be a good person? I know that for me, I feel better believing that I am not actually good, but that I'm trying to be. I feel that holding on to that idea will serve me best. And it doesn't hurt to remember that other people are also often just trying to be that better person in their own way (or at least I hope most are, some obviously don't consider it at all). Of course people will disagree about what that looks like for themselves and others. Empathy isn't an end or a given, it's constant work.