I'm sorry but I'm really having a hard time understanding your reasoning here. Are you really suggesting that the majority of people on HN who are defending the right to free speech of the neo-Nazis we saw in Charlottesville are doing so because they actually agree with the message those neo-Nazis and white supremacists are spewing? If this is what you believe, then please just come out and say that anyone defending this type of speech is in fact a neo-Nazi. You talk about mechanisms that undermine an honest debate but in the very next sentence you essentially argue that anyone in support(I'm adding an edit here to clarify: I mean support for the right to this kind of speech, not support for it's actual content) of this kind of objectionable speech is a Nazi in disguise. That certainly seems like undermining the debate to me. I don't like this kind of character assassination in disguise. Either be willing to call people out as Nazis and white supremacists, and back up your assertions, or give them the courtesy that they might be taking a stand in defense of a principle they actually believe in regarding speech, even in cases where they disagree with contents of said speech.
I personally don't believe a reasonable person can be a neo-Nazi and thus I have very little interest in arguing or engaging with these types of people. When it comes to free speech I tend to fall on the side of having fewer restrictions on speech, although even here my views aren't really set in stone and do change on occasion. With that being said, unlike my views on Nazism, I do think reasonable people can disagree on the issues of where to draw the line on speech. Again, while I personally fall into the less restrictions camp, I don't think its unreasonable for someone to want restrictions on certain types of speech and thus I don't automatically assume those arguing for these restrictions are authoritarians in disguise. If you think this makes me a neo-Nazi I would prefer you just come out and say it, this is of course in the interest of "honest debate".
Edited for spelling and grammar.