I love when they always pull out the argument: "o-oh, well, sexual orientation labels are actually voluntary to use, so get lost! people can describe themselves however they want!"

Yup, indeed they are. I, for example, could call myself straight 'till the cows come home. Doesn't the change the fact that I'm not fucking straight lol.

The labels are perhaps voluntary (that's even debatable), but existing in a state which fits the descriptor of 'lesbian', 'gay', or 'bisexual' are not. No one has volunteered to be whatever sexual orientation they are. Stop appropriating and stealing descriptors that describe our body's responses to both males and females when it comes to romantic and sexual attraction.

Like, I don't see how this could be any more obvious.

'Gay' is not a descriptor that transmen can use if they are attracted to males because they are not a male attracted to exclusively other males.

'Lesbian' is not a descriptor that transwomen can use if they are attracted to females because they are not a female attracted to exclusively other females.

Objective reality exists and we use words and descriptors to describe said reality and share our experiences with others in a way that is elaborate and straightforward. Attempting to rewrite these descriptor's definitions to include a variety of other things is not only homophobic, but regressive.

EDIT: Words.