The reason why this problem exists is because conservatives believe in freedom of speech and live and let live, whereas leftists believe that certain ideas are evil and those who espouse them must be routed out and destroyed.

Thus the freedom to let leftists exist is the freedom to let leftists destroy you.

The only solution is to ban them altogether. Not because you want to control them but precisely because they want to control you.

This has been proven time and again throughout history.