Why The Name Calling of Opposition?

I see this so much in adults, grown ass men and women, people who are college educated, self-educated and so on. I see it extremely heavy in politics it’s just ridiculous. Why is it such a challenge to step back and acknowledge that this behavior is immature and petty as High Schoolers. I realize full grown men and women act like children too, even in situations that render intelligence, critical thinking, respect and understanding of both sides and most of all humanity.