That’s an extreme response. Why not ask what they mean by that? Understand their viewpoint? Treat them like a human, flawed as they may be, just as you want to be treated as a human.
All banning them does is isolate them, encourage them to avoid interacting with others and so have a limited and isolated worldview. Sure you don’t have to let them abuse you, but defeat their ignorance with kindness, not force.
Yeah. "In your ideal future, why do people like you still exist?" IS an extreme response.
Thankfully we understand it perfectly and can block, report and move on.
Like, let's not minimize what you're suggesting here. This person not only thinks LGBT people ideally shouldn't exist. They take for granted, as obvious, that WE don't want US to exist either. And you think we should treat this person like a human?
Okay yeah, I'm going to treat this person like an adult and not coddle them like an infant. That would be disrespectful of me. I'm going to value my own mental health at least as much as theirs, because we're both humans. I'm not going to pretend that they didn't just imply that I shouldn't exist. I'm going to do what humans do when other humans insult them: I'm going to be insulted.
If they need to LEARN that I'm a fucking human being, they're in luck! I support queer representation in media, which normalizes our existence and fights against the stigma that was implanted in SO many people (us included) growing up. That's going to do more than me holding a bigots hand, treating their position as if it has ANY value whatsoever, and gradually convincing them that I have an inner world.
I TRIED that, with someone I considered a close friend. Maybe it's possible. I know it hurts, a lot, and I didn't have the self-confidence to pull it off. I learned more self-loathing from him than he learned tolerance from me. If I had spent that time seeking to understand myself rather than trying to manipulate a bigot into being a good person, he and I would BOTH be better off. I did him no favors by being his token gay friend, and humoring his shittiness. I only emboldened him.
Again, the better strategy is to live well (and as openly as you can safely do so)... and to respond to open bigotry with social consequences. That's how society works, and it's the respectful response. Bigots ARE humans, not infants or robots, and they're responsible for their actions. Bigotry thrives when it's humored, and shrivels when people express disgust at it.
Edit: Because to be clear: self-harm is a problem in the LGBT community. Because we've been taught to hate ourselves or *at best* to wish we were "normal". That's highly internalized, particularly the older the person is. That's not an impulse we can AFFORD to humor. It NEEDS a stern rejection, both internally or externally. (it's an incorrect impulse, implanted by intentional media campaigns AND BIGOTS MAKING JOKES, and it's very deeply installed.)