Men adopting feminine appearance and/or behaviors make others in the society question his will to live up to the duty of protecting the society from attack. It's assumed that females are both physically weaker, and as nurturers potentially less likely to kill an opponent. That could make the difference in a society surviving, or not. Although we've outgrown those times, the instinct is still in our dna. Sure, some can 'think' past the initial impulse, but not all people are that smart, and they're much more comfortable living day to day with only basic urges directing their life. Witness the huge numbers of people who embrace Beavis and Butthead behavior. Idiots enjoying behaving like idiots. Any wonder space aliens won't contact us.......