I mean I could be not attracted to people with a mole on their stomach and not find out about that until later even if I was initially attracted to them. I could also be attracted to someone until I found out they were being targeted by a stalker and then lose my attraction to them because of that.
You're saying that you cannot choose to not be interested in a trans person if they successfully pass and therefore you don't know in advance without that being transphobic, despite a) who you are romantically attracted to is a deeply personal choice and b) being in a relationship with someone means their life heavily effects yours. People avoid others romantically for life difficulties that aren't even their fault all the time (nasty exes, legal or money trouble, etc). Wanting to avoid potential issues associated with being trans, even though none of those are the trans person's fault is the same thing.
I think you're going to have a really hard sell to lay claim to what people are and aren't allowed to feel about potential partners. You might get people to give lip service to it, but I doubt you'll get people to have true buy in to saying they aren't allowed to feel certain things in regards to potential romantic partners. That's a pretty extreme take in my opinion.