We in the sex-positive crowd generally treat a person’s sexual and gender identity and sexual tastes or habits as a black box. For those who haven’t heard the term before, a black box is a term of art referring to an unknowable process. You don’t know how the black box produced this result, and you can’t find out, so just take the result and get on with your work. How did a person come to be a serially monogamous cisgendered lesbian who likes her hair pulled? How did this other fellow end up as a straight male top with a taste for leather? We don’t know. They just came out that way, and you should be polite to them.
We do not treat sexuality as a black box because it actually is intrinsically unknowable, but because it’s the only way we can have a civilization.