I’m an anarchosocialist, not a neolib. Don’t “*I* will be forced to fight them” me, like you’re some kind of hero. Their ideology is already out of date for being morally wrong, saying genetic technology is what will end them implies that the genetic “problems” they present actually need solutions. Violence against fascists is the only option against fascists. They cannot be debated since their ideology is grounded in hatred not logic, they cannot be appeased as they will always ask for more, they have to brutally crushed/scared into disbanding. 
And while fascism is rising in America, antifascism is rising much faster, and hopefully they will come to an inevitable conflict in which fascism is finally wiped from the earth. 

1. The strategy of street fighting the Fascists in Germany failed so badly that Hitler came to power and nearly took over Europe.  If he had been a bit more competent he might have succeeded and the Third Reich could still exist today.  This strategy has already been tried, and it already failed.
   
2. Antifa have pepper-sprayed bitcoin enthusiasts, destroyed immigrants’ cars, harassed business students, and so on.  If the violence were limited to just actual fascists/WNs it would probably be possible to get away with it.  It isn’t.  Instead it’s playing right into the hands of groups who say that “no white is safe”.  By all appearances, Antifa like punching and the feel of righteous indignation more than they value actually bothering to check who is and is not an actual Nazi before punching them.  This makes people who are not Nazis suddenly very concerned about the safety of Nazis.
3. If someone is converted to Fascism, there is no reason to think they cannot be deconverted from Fascism.  There have already been very successful attempts to deconvert Klansmen, who you would very likely claim are also motivated entirely by hatred and must be destroyed by force.  Deconversion is morally preferable to extermination and also results in ideological evaporative cooling, leaving only the craziest members who will seem less credible.
4. Deconverting them requires the ability to make credible claims that there is not a plan afoot to demographically replace them.  You, and the Democratic Party, cannot effectively make this claim.  You probably think that the rise of Trump is a scathing indictment of American racism, and not the result of a direct correlation between premature death rates for middle-aged whites and % Trump votes on a county-by-county basis.  There are a number of large holes for rival ideologies to exploit which could have been prevented entirely by buying off the white working class (and so on), but the Left was not politically willing to pay the cost of closing them.  The mainstream Republican establishment wasn’t willing to pay them either, which is why they got knocked over like a bunch of bowling pins by a populist with little political experience.
1. Not to mention that a lot of the pro-diversity ideology is contradictory or implicitly accepts some of their frame, as I have specified.  People can notice the hypocrisy.  It went under the radar when there was less stress in the system, and in fact I quietly supported keeping it under the radar in order to keep the amount of racism low (this is after all a multiracial country), but all of these terrorist attacks in the West have blown the lid off.  New ideological tools must be developed to repair the situation.
2. Speaking of ideological tools, some old ones must be revived.  The cultural mosaic model creates ethnic tensions.  It’s time to explicitly bring back Melting Pot.  Not bringing it back just gives people reason to wage culture war for the supremacy of their own culture.
5. With advances in genetic technology, white nationalism becomes largely obsolete not just on the premises of its opponents, but on its own premises.  Most ideologues these days are not effectively dealing with the looming spectre of Transhumanism that is due to arrive within decades.  Nervous-system-controlled robotic limbs, vat-grown organs, and genetic selection technology are already here, they just aren’t up to par yet.  Most ideologies will have to be changed significantly to accommodate.  The reason I brought this up is because, while it’s a weakness for the mainstream, it’s a much more glaring weakness for WNs that is not being adequately exploited.