>>3264 (OP)
I don't think they're strictly gay, they just fuck anything they want, whenever they want. I think in terms of the original universe vs. the mirror universe is meant to be something of a left brain vs. right brain, on a cosmological scale. In the original universe, the actions of nearly every character is based a bit more on intellectual motivations. Even the seemingly more primal species, like Klingons or Naussicans, do what they do more in a culturally motivated way, as opposed to doing things instinctively. Even humans, who while traversing the galaxy have the tendency to fuck half the species they encounter, still operate on the basis of intellectual and cultural exploration.
The mirror universe, on the other hand, thrives on primal desire. Every motivation is pointed directly inward, and everything is done for either personal gain, or physical pleasure. Intendant Kira is a perfect example, she isn't necessarily a lesbian, she'll fuck anyone she's drawn to in the moment, while still ensuring that she maintains military and political power, so that she can continue to do and fuck who/what ever she wants. And since nearly everyone in the MU chooses to give into their primal desires, they've all turned into perverts. Look at modern day gays, they've been given free reign to be as gay as they want, so they take it to the extreme, constantly seeking more and more pleasure. They don't even bother to keep it behind closed doors anymore, they dress like women, they have their parades, I've even heard of some gay event in California (where else?) where they are actually allowed to perform sexual acts on each other in the streets, out in the open, legally. That's why everyone in the MU is bisexual, they embraced their primal desires and allowed everything to get out of hand. They're all degenerate perverts.