The correct response is for the government to treat domestic terrorists, and preachers of hate the same way that they treat foreign ones.
Anwar Al-Awlaki, and his son were the targets of a US drone strikes for the same thing - radicalizing speech, and inciting terrorist attacks. Yet, here we have an entire ecosystem of alt-right radicalization, inciting terrorist attacks, and the government doesn't lift a single finger to deal with it.
So the right wing white supremacist problem, at least in the U.S., has been taken seriously; but with political change it has been taken less seriously by the current administration, for entirely predictable reasons. Whether FBI takes it seriously enough is an open question, but when intelligence agencies publicly list threats to the U.S., the southern border is not on the list, but right wing white supremacist hate groups are.
There is a very real issue that until there is planning or solicitation to commit violence, right wing white supremacy is legal freedom of association, and hate speech is still protected speech, so long as it's not in the gray area of "fighting words". I think it's completely reasonable for FBI to infiltrate violence prone hate groups by paying informants and putting agents on the inside. I also have no problem with enduring warrants on leader organizers of such individuals for wire tapping. What they want is a race war. They want to destabilize the country. It's not a new thing.
ADL and Southern Poverty Law Center have been tracking hate groups for a long time, both left wing and right wing. It just so happens right now it's overwhelmingly right wing hate groups out there. And it would not surprise me if the more violent prone ones would love to see successful recruitment of left wing groups, because they can't really have a race war, or make real their romantic notions of a civil war 2.0, with just a bunch of right wing groups. They have to incite the left to attack, or they've got nothing.