That's just a completely different aesthetic, man. It's not in any way equivalent -- just like a FFM threesome is harmony and loving, whereas a MMF threesome is violence and degradation. I'm not saying it's "wrong"; just a different aesthetic, is all.
My gf actually has this fantasy about me screwing a male K-pop star. Needless to say, I'm not into it. But it's just a fantasy, because she understands I'm straight while she's bi.
So, we agreed on my suggestion that it would be better if she made out with a girl and I watched, maybe joined in.