I agree. As much as I am amused by punching Nazis, sucker-punching them is certainly the wrong way to go about dealing with them (though I joke that the puncher should be charged with a crime, the punishment should be community service, and punching Nazis is a community service, so it's a wash). That said, if the Nazis or any other hate groups actually start acting threateningly and escalating the situation, I'm all for punching them in self-defense.
I wish I could find the link, but it was the story of a now professor at Cal Berkeley who was a student and a protester there back in the 60's. There was a Nazi who came to speak on campus back then, and instead of violent protesting outside, there were a bunch of anti-Nazis who actually watched his lecture. During the Q&A session at the end of the talk, they grilled him so badly with pointed questions that he came out looking like the total buffoon that he was. Said professor argued that this was a better way to deal with Nazis peacefully than just yelling and raising hell or even preventing them from speaking -- confront them peacefully, but directly, and let them expose themselves for the fools that they are.