Activist-somebody loud with an opinion they want opposed upon others
They also have absolutely no understanding of the topic they claim to know about.
My personal favorite is “Food Babe.” She has a degree as Computer Science and is a “self-taught” food scientist who goes after major brands to get them to remove ingredients she had determined are bad. She also believes that saying “Satan” to a glass of water will chance it’s properties and a microwave will do the same thing, so therefore microwaves are bad.