It's indeed a very tough one, as simply 'ignoring it' gives rise to the idea that these are acceptable positions and that people can attend these events and celebrate these positions with no fear of repercussion to themselves. That's seen as dangerous, as it would essentially be our society accepting these things as 'normal' ideas when they are anything but; and what more, accepting the idea that these are not in fact scurrilous, anti-American and dangerous ideas.
So, do you push back against them with direct protest - giving a clear signal to all that these ideas are not acceptable ones to promulgate in our society - or ignore them? What does ignoring them do? Many would have us believe that people like Spencer would wither or go away if they just were ignored, but I think that's totally and completely ahistorical and wrong.
The right-wing is using assholes like Spencer to weaponize free speech, and turn it against the people of this country. I really don't know what the answer to it is, but I can't imagine ignoring it is the answer.