I mean any argument towards an imagined concept is relative nonsense. It's just people tossing around their understandings of the undefined portions of a concept.I really hate the 'if it has a dick and you have a dick, it's gay' argument. It is such utter nonsense, especially with futa because the futa genre is all about girls, specifically girls, with dicks. It's automatically not gay if there is only a girl involved and you aren't a girl.
You're over generalizing bits of it. You could very well say a guy is "just" a girl with a chromosome swapped out, making you a lesbian no matter what.
The thing is isolating and focusing on the fact that there's a dick and seeking out porn of that fashion means you're interested in the dick. No ifs, ands, or buts (plenty of dicks though). Really though, it's not Female or Male, but either both or neither making it equally as gay as it is straight.