I think it's pretty basic.

Bi females are still "available" to the jocks, so it's just a little kinky.

Bi men introduce chances that they could pass on to women devastating

diseases that can compromise the availability of women, thus are bad.

The biggest fear for some is that in a threesome, they could become "piggy in

the middle" and enjoy it, making them something they hate, with ego consequences.

__________________
Calm, quiet, smooth, devastating