I see this topic, the main one in the thread, so interesting. Because, in the end we are social animals as you said.
I do understand that the deeper and harder your experiences have been, the tougher you will find to trust people. As an extreme example, see these kids who have been neglected or even abused when kids.
How could they trust or even picture themselves that someone is gonna care?
Ok. Consider that even the parent who neglected his/her kid ( with only few and pathological examples), they are not a basket-case. They did it the best they could under their circumstances.

Each person deal with their life as best as they can. They may fail and even let you down but believe me they don’t do t on purpose. They react as they can as we do. You who knows much more about Psychology for obvious reasons and also because you love to study how others behave (as I do), you can understand them better than most of people. Use this skill. Make it matters.