Imagine you're a 14 year old girl.
You've begun to realise in the last year or so that you are sexually attracted to women's bodies, and sexually turned off by men's bodies.
You're also aware of a whole load of other things. That there's a name for what you feel - lesbian (or in the mouths of some of the unkind kids in school "lezzer"). You know that some people are okay with that, but others aren't. Some people are so "not okay" that they might beat you and your girlfriend up - you saw the front page news coverage of the two lesbians on the bus. You know that parts of society are repulsed by your sexuality, and also (because the boys in your class get a lot of fun waving mobile phones with porn videos under your nose) that significant numbers of men fetishise your sexuality and think it's all a big performance especially for them.
So, as if adolescence wasn't confusing enough (and it's pretty damn confusing, even for your straight friends), you know it's a hundred times worse because on a bad day your sexuality is variously seen as abnormal, unnatural, wrong, something to be beaten out of you, or something that exists for the entertainment of men.
And now the BBC - the fucking BBC, with the massive amount of cultural capital and authority they carry just in virtue of history - comes along and tells you "lesbians are same gender attracted", so your lesbianism must include penis - the thing you know you're not attracted to - or you're doing it wrong.
Or even worse (because you note all the stuff conflating crude sexist stereotypes and gender identity, and you also note that "straight" people seem to still be allowed to discriminate on the basis of genital arrangement without being told they're bigoted) you decide the only way you're allowed to be exclusively attracted to women (the biological, cunt-owning kind) is to announce you're in fact a "straight transman."
Fuck that shit, BBC.