Do you honestly believe that someone who posts a misogynistic meme is an extremist or is it hyperbole? I personally would reserve the term for someone who commits violence out of some ideology. I never thought to look before but the first definition from a DDG search says something that would put a very large number of people into that category;

>A person who advocates or resorts to measures beyond the norm, especially in politics.

Someone calling for UBI five years ago could be called an extremist. Though it does need someone to define 'the norm'.