So often because those who enforce the the law aren't willing to do their job and protect people. Case in point - the police in Charlottesville. They didn't protect that town's citizens from a bunch of white supremacists marching through the place and killing or injuring people. If Antifa are 'extremists' for being violent towards neo-Nazis then it's a label I suspect more people would wear with pride. Neo-Nazis like Richard Spencer call for the killing of 'undesirables' (in Spencer's own words, it's 'peaceful genocide') and so often the authorities turn a blind eye when it matters.
If a neo-Nazi attacked an Antifa member unprovoked I presume you wouldn't have a problem with that Antifa dude hitting back in self-defence; so why would you take issue with him using violence against someone that's calling for people who are likely their family, friends or even themselves to be killed? Also, where's the evidence that Antifa
started the violence in Charlottesville? It's worth bearing in mind that some of the white power trash came loaded for bear - they were better equipped than the police and were looking for a fight.
Neo-Nazism does not invite rational discourse nor accommodation because it is itself irrational.
I'm not an Antifa fan myself given that they sometimes proclaim ex-Muslims as 'Islamophobes'.
I have a better idea, why don't we throw all the white power freaks, neo-Nazis and other members of the 'alt-right' (using the term ironically here) into gas chambers? Give them a taste of what they call for every time some drunken skinhead changes the lyrics of a song to 'gas the Jews!'.
And, true to form, we now have
Alex Jones of Infowars calling the white power marchers in Charlottesville 'Jewish actors' trying to frame the far-right.