Certain selection bias there - we only hear from the dumb people who are dumb enough to demonstrate their stupidity loudly. Though perhaps the sense to shut the fuck up is itself a sign of a certain level of intelligence that’s missing from the even dumber ones.

Empty vessels make much noise

A good argument only needs to be said once.

A stupid one needs to be repeated over and over until it hits an ear stupid enough to believe it.

The best lack all conviction, while the worst Are full of passionate intensity.