Karl Popper discusses "unlimited tolerance" which literally no one is demanding. With very very few exceptions, we all accept limitations on speech. We have specific exemptions to free speech like incitements to violence for this reason.

Popper also states: "I do not imply, for instance, that we should always suppress the utterance of intolerant philosophies; as long as we can counter them by rational argument and keep them in check by public opinion, suppression would certainly be unwise." He only recommends such an extreme action when all else has failed and we're up against "fists and pistols". When hate groups are committing acts of violence (not just acts of speech), the US is certainly not sitting around tolerating that behavior.