I feel like both sides could mature a little. "Grill" is just a common joke, it's not meant to be offensive. But, at the same time, stuff like "The internet has no girls" should go away. It's especially bad in MMOs, a genre that a lot of girls actually play, that has the joke where every girl is actually a boy in real life.
Also, yeah, coming out as transgender would be hard due to this. Although, I'm not too sure about how genders work since when I think about my own gender identification my mind just goes kablooey from confusion.
"There are no girls on the internet", and a similar one I'll get into later, are two of the most commonly misunderstood phrases I've seen. It's not to erase women, or to tell them they're not welcome, or any similar nonsense a certain infamous plaid shirt fan with hoop earrings might tell you. The phrase "There are no girls on the Internet" is a reminder that gender is irrelevant here.
Back in the earlier days of the net, this was closer to true. It was mostly a place for friendless nerds. So, when somebody showed up claiming to be female, they got a lot of extra attention and an army ready to come to their defense whenever somebody started giving them **** about something. In MUDs and MMOs, this person, whether they were truly female or not, would often get invited to more questing groups or got free stuff from lonely, socially ******** men. "There are no women on the Internet" was a phrase used to remind people that, statistically speaking, this person was probably a Guy In Real Life, and becoming a white knight or giving free stuff was dumb.
Its sister phrase, "**** or gtfo" is used to remind a "girl" that this is the Internet and gender doesn't matter. All that matters is what you can bring to whatever platform you're a part of. If you're good at this game, that's all that matters. If you can contribute to this fansite, that's all that matters. We don't need to know your gender, like we don't need to know your skin color or what you eat for breakfast. It's irrelevant, and due to the history surrounding people randomly announcing their gender in virtual spaces, there's probably a motive behind it.