If you think about it, they are denying people having different romantic and sexual orientations, and set up that being lesbian is having sexual and romantic attraction for women.
They also gatekeep lesbianism as a whole, while lesbian is no longer an umbrella term, not everyone has all ranges of attraction toward women. And saying "lesbians can't date men" to an m-spec lesbian is in it of itself invalidating their single range type of attraction. Which is pretty harmful, not everyone needs to fit the perfect cookie cutter of matching romantic and sexual orientations.