Don't we all struggle with this? You want to believe in the best of people. You try to find the good in everyone. Yet, we all suck a little bit. Okay, some a lot.
I'm reading here in my management textbook about nonreligious spirituality and how Christianity differs. Nonreligious spirituality says that "all humans are intrinsically good."
I remember hearing in Sunday School a very easy counter-argument for this. Little kids never have to be taught to misbehave. No, instead we have to instruct them on fairness, sharing, and respect. You never have to teach a child how to be selfish, rude, and disrespectful.
So I guess it's all about how you value people. Because yeah, the Bible says that we are by nature sinful beings, our hearts are deceitful above all things (Jeremiah 17:9). But yet, we were made in the image of God, and through His power we are able to do good things. Only through Him. All people are good because God said that we were when He created us. He cares and loves each and every one of us selfish, cold-hearted, and deceitful people so much that He came down as one of us and died. People are all God's creation, God's children. Yet we have this sin nature that tempts us to do bad all the time. So why do we always say that we have to find the best in people?
I think it's because if God can love that person, we can too. The least we can do is care about someone that God cares about. And maybe that person will come to love Jesus because you loved them. It's pretty cool.
The good in people is that they are all created and loved by a good, Holy, and merciful God.