The main problem with humanity is unawareness.

Ehhh.

The worst problem is we weigh in-group status more than facts. We evaluate situations based on in-group fidelity and emotional shortcuts. That's why you can't change someone's minds with facts. People almost only change their mind when it's from in-group influence.

We all do this to some extent. You're more likely to listen to someone you trust than a stranger. You're probably more likely to trust a stranger that looks basically like you.

But yes, the defense mechanisms people have to protect their ego is part of the problem. People will go to great lengths to protect their sense of self. The Oatmeal has a comic about it: https://theoatmeal.com/comics/believe