Why stupid people think they're smart.

The Dunning-Kruger Effect.

Why incompetent people think they’re smart.

Summary:

They see one study about one side of an issue and form their biased opinion based on that one study. That’s not how science is done. Science means we look at both sides of an issue and get multiple studies to study the issue with more depth.

But because they only look at one side of an issue, and their knowledge is shallow, they cannot explain the concept behind what they talk about. IME they cannot produce a link to any study at all.

Here are some interesting videos on the subject. I happen to like how Afterskool approaches these speeches. He gets permission to use someone’s speech then animates it for visual effect.