The solution is to convert them, all of them, even the marxists.
Do you know that Dr. Sowell was an avowed marxists during his college years. He became one of the leading lights of conservatism through real world experience and talking to conservative. I believe many conservatives have had the same experience.
Exclusion is not the answer.
Some can be converted. Others don’t want to face reality. If folks aren’t willing or able to understand, they can’t be left to screw others up. We need to tell them to go somewhere else. And I count members of my own family among that group!