True, but people are like that. They sin, even Christians.
This life is basically an unfair, monstrous nightmare where evil wins pretty much every battle. The promise of Christianity is basically good winning the war at the end.
It takes faith to believe in God? No, I don't think it's matter of faith at all, since the natural can't be the first cause of natural; the supernatural, which would be the broad definition of "God", being a sine qua non condition to the natural existing.
It takes faith to believe God is good? Yeah, I admit it does, and at some moments, pretty much every Christian doubts it. But again, we don't have the whole picture. Truth is, humans are weak and falter at things pretty easily.