So it would have been great to kick out all the professors who spoke negatively about some aspects of U.S. policy in the 50s because they were "communists"? Would have been great to kick out all the professors who supported the civil rights protests of the 60s because they were giving arguments for the validity of civil unrest? It would have been good to kick out physics professors who were advocates of nuclear power when nuclear power was at its least accepted?

I think not.

History shows that we are bad, at the time, at judging even what is correct and not, let alone what is reasonable disagreement and what is unreasonable. Having a place for the unpopular voice that needs to be heard is very important, and universities are a great place for that. We just have to accept that a lot of the time, that unpopular voice will be wrong. But we can't hear the critically important ones without suffering through the bad ones.

Tenure is fine, as long as we have mechanisms to limit any damage that a particularly problematic person might deliver. (Penn has such mechanisms and has employed them.)