Yeah, I don't know why this is a debate. LGBTQ+ ally my whole life, though I'm cis/straight myself.
I almost get it. Like the fear that you hook up with a girl and she has boy parts. It's not really reasonable but it's a common male fear, I guess. Like she's gonna be so convincingly female, so perfectly female presenting but she hasn't had the bottom surgery. I think that's kind of a fantasy, because pass as the sex a trans person feels isn't as easy as cisgendered people think it is. I have trans (MTF) friends, and they do not pass well. Oh, I fully accept that they are women; what I don't do is assume I'm entitled to every female body, or for the female bodies I have access to, to fit into my potentially narrow view (it's not narrow, but if it were) of what makes a woman attractive. At the end of the day, she's a person and her body is what it is, take her — as a complete person — or don't, but don't waste her time and definitely don't think you can shame her for it. And it absolutely don't mean she's any less a woman. That, I do feel strongly about.
Also, I've known a couple tomboys, girls I grew up around who weren't conventionally pretty, who liked to play and fight with the boys (and they'd kick your ass, too), and the older adults said "oh yeah that's a baby butch right there" and later, when trans people became more visible to us (I'd say late 90s early 00s), the assumption that she's gonna transition. Going on like 30 years later, they're still girls and they're still straight (and the one I'm thinking of, definitely wears the pants in the relationship, her guys tend to be kinda meek) but that doesn't mean she's gay or trans. Oh, plenty of LGBTQ+ in the family, but you can't say because a girl doesn't like pink and doesn't like dresses that she's lesbian or trans. It doesn't work that way. But as her peer, as her playmate, and often as one whose ass she'd kick, I didn't care. I love her for the person she is, not for the box society puts her in, or checks for her. And if she did bring home a girlfriend, or if she did tell me she never felt like a girl and was going to transition... my sister (not really but like a sister to me) would be my brother or whatever and that would be okay with me, whatever the case, and I'd have their back regardless.