I denounce Nazis, White Supremacists, and other alt-right extremists, and with the same fervor and conviction I denounce ANTIFA and the alt-left extremists. Both are populated with bad ideas and use bad tactics to promote their bad ideas. I find nothing redeemable about either of them.
Those who don't learn from history are doomed to repeat it.
A similar dynamic between similar groups played out in the 1930's between the Red Shirts (Communists) and the Brown Shirts (Nazis) resulting not only in the Red Shirts loosing to the Brown Shirts, but also swinging the sentiment support of the electorate to law and order, which the Brown shirts promised them, hence, making the Brown Shirts even more popular with the electorate, antithetical to the Red Shirts stated goals.
I think Ben has it right on this one.
Shapiro At 'National Review': America Has Twin Cancers, Antifa And The Alt-Right
I further think the each group should be given their rights, and to exercise them, as legally required, but if either steps one toe over the line, even the slightest minuscule legal infraction the perpetrators need to be arrested, charged, held without bail, and tried.
A civilized society has no use for either of them, and has no need for a repeat of WW II.