Jealousy is at the heart of the current trend of hatred against beautiful female characters in games.
Men and women are genetically programmed to seek out better, healthier and younger partners and they know it. This is what makes them extremely jealous of anyone of the same sex who is physically superior or successful to them.
For example take a middle aged couple, the wife walks into a bar and sees her husband sitting next to and talking to a young female super model. What are her first thoughts?
A. That cheating bastard!
B. Probably just another bar patron.
Of course her immediate thought is that he is cheating on her with this girl by simply talking to her.
An easy example for men is Justin Bieber, men are extremely jealous of his success and how women throw themselves at him regardless of his lack of musical talent. This is what has lead males to hate this guy and other popular young male singers and boy bands.
Due to the advancement of graphics game characters can look extremely realistic and beautiful. Men and women are spending more time than ever interacting with digital media rather than with each other, whether it be phones, tablets, consoles or computers. Women see that these female digital characters have far higher sex appeal than they could ever possibly hope to achieve with their unrealistic proportions and perfect skin.
Women become jealous of the digital female characters who are stealing the attention of their mates or potential mates. Finding they cannot change the hobbies of males they've pushed for sex-negative campaigns against digital female characters to try and stifle their sex appeal and hope to receive more direct attention from males in return.
The men joining the cause are simply doing so to be seen as apathetic and gain attention from the women.