It happened a lot more often back in 2012 when he was running for President.
Meanwhile Richard Spencer's Wikipedia page starts with "Richard Bertrand Spencer (born May 1978) is an American neo-Nazi..." It is entirely fair to call that guy a Nazi and it is the reason the modern "punch a Nazi" meme centers on him.
But I must beg the question, if society normalizes and encourages violence against Nazis, doesn't that mean that calling someone a Nazi is a potentially serious act? And, what if they aren't really a Nazi?
The term "stochastic terrorism" has been discussed and I believe it applies here. This is the definition I pulled from dicitonary.com: "the public demonization of a person or group resulting in the incitement of a violent act, which is statistically probable but whose specifics cannot be predicted"
Context is important and it seems like you are trying to blur that context for the sake of an argument. "Mitt Romeny is a Nazi" is not a serious opinion. "Punch a Nazi" is only a slightly more serious notion, but there is firmly a tongue in cheek aspect to it. There is a reason why the only "punching of a Nazi" to reach any type of penetration into pop culture was from the year before this Kickstarter was launched. This comic is not a serious threat anymore than your average issue of The Punisher.