Not all humans. Many, many, I have been around a great deal of awful people. I have been around even more decent people.
I find the trouble is that the awful people(people who let you down, only look our for their interests, are unreliable,) are tolerated by decent people. Even when said bad person is slowly but obviously ruining a good thing. People shrug, they don't want any conflict until it's too late.. I once removed myself from an organization because I predicted what would happen to my friend who wanted me to stick around. My predictions came true, but it did not cause my friend to say. I should have listened to you at the beginning. He admitted I was right but showed no remorse for allowing it to happen.
While negative thoughts bombard me.. When my mood lightens, I still have an optimistic outlook for the world. Not for me of course. Take care as well as you can