I dont think suggesting transphobia when it comes to sexual preferences is appropriate, people can't choose those any more than they can choose to be black or white. There are also simple biological facts, perhaps a person wishes to have biological children with their partner. Or any other reason really, romantic preferences are entirely subjective and often not even a conscious preference.
That being said, i think a good compromise would be for people to be able to give these kinds of personal preferences to the dating site, similar to the age ranges they want to encounter. Then the system would automatically prevent incompatible preferences from getting matched, and nobody has to out themselves.