I think female characters attract the most criticism because they are the characters that people want to get right most of all. People want female characters to be strong physically, mentally, and emotionally, but at the same time, not bitchy or whiny. If any of these features ever creep up, audiences are all too quick to shout 'sexism' or 'stereotypical'.
I never found this to be the case. I certainly have found that there are not enough lead female roles, which I think is sad, but I typically dislike a character because they have a trait that I dislike, not because of their gender. If you look up Walking Dead memes, I think you will find just as many Spaghetti Tuesday and dissing Dale memes as you will Lori memes, I could be wrong.