It's the idea that people on tumblr have a tendency to "fix" picture by making them representative of those who aren't as "physically attractive" as what's societally "acceptable." While I get it's because they hate not being represented in media as much as they could, forcefully changing something and then calling it "fixing" (implying the artist is wrong) is kind of upsetting because of how much effort the original work usually has put into it compared to the "fixed" product