Why is F2F seen as socially acceptable but M2M is seen as evil?

[ESLteacher]

Straight men find is very sexually exciting to see two women get it on, but their ego tends to block the reality of two men getting it on and it tends to disgust them. Women tend to be more open minded and can appreciate the beauty in another woman, even if they are not interested in them. Unfortunately it is still a bit of a straight mans world out there.