Extraordinary claims demand extraordinary evidence. Bisexuals exist and aren't always obvious, so "absent evidence to the contrary, that person might be bisexual" is not an extraordinary claim — hell, assuming similar prevalence of bisexuality then as we see now, which is arguably the lower bound given the cultural changes depicted, it's statistically improbable that there wouldn't be at least one non-straight person in the main cast.
I don't need to know their exact sexual preferences. That is not of any influence to the story. If it was, it would have been in the story and if it was in the story, it wouldn't have mattered what their preference was, because it would have made sense either way in the context of the story.
Issues of sexuality and gender are already being adressed in this show, there is no need to project them into situations where they're not.
Right, but that's a completely different thing than you were arguing. The likelihood of a character being queer is a Watsonian question about demographics of a space station, whereas whether it's plot relevant is a Doylist question about themes and conservation of narrative. And given that Garrick was originally conceived as a queer character and the actor has explicitly stated that he wanted the character to be queer, but Rick Berman insisted that this not be done and instead wrote in a weird love story between him and young girl, I actually think it's pretty f****** relevant to discussions around the culture of the show.