I've been thinking about the "nerd blackface" thing...

Let me be clear up front here, I think it's disgusting when people use the term. But a question did pop into my mind a few minutes ago, and I thought I'd pose it as a discussion topic.

Why do we all hate it when someone uses the term "nerd blackface" (which I do), but no one ever seems to bat an eye when someone uses the term "grammar nazi." They're almost exact parallels. "Nerd blackface" says that the people making The Big Bang Theory are just as bad as actual real life racists who ran extremely offensive, by modern standards, shows making fun of black people. "Grammar nazi" says that people who have the audacity to correct minor (or major) grammar mistakes are worth comparing to people who murdered millions of people.

I'm not saying this to judge people for using the term, or to complain about it, I've probably used it myself before (although I've always thought there was something skeezy about it, so not much), I'm just curious what thoughts people have on the subject.