> Do you think that the LGBTQIA+ community is best served in this method?
Ideally, there would be dedicated spaces because the existing spaces are generally very hostile. For example, it is common for people to create fake profiles in order to get past the first layer of verification (looking at the profile and reading the required questions). Once in, they take pleasure in contacting members to push them to suicide. Online trolling with real dangers.
There is also the fact that the mission of the platform is generally not very compatible or at least the lack of attention to the LGBTQIA+ communities creates such negative experiences.
For example, Facebook's automatic moderation detects ordinary slurs but not targeted homophobic or transphobic slurs or "dogwhistles." This often results in a troll using something like "you'll never be a woman" or calling transgender people "the 41%" or "join the 41%" (in direct reference to suicide rates).
Understandably, users get frustrated and tell these users to go away using harsh words, and also report the troll to Facebook. What usually happens is that automatic moderation does not detect the troll, responding that the comments do not violate their terms of service. However, "griefers" often report legitimate users. The recent changes make this very easy, as something as innocent as writing "why is this man here?" in a space dedicated to lesbians will be flagged as hate speech against a gender identity. Thus, the troll gets away with it and the users are banned for 30 days by the platform. Often, a troll can manage to flag enough comments to have entire groups shut down by the automatic moderation tools.
This makes these spaces unsafe for supporting vulnerable people. For example, one public page that I have access to the admin panel has such a large ban list that I'm not able to get the exact number without the admin page crashing. By playing with the APIs, I was able to get a count of 25k bans before it also crashed and returned errors.
But as you said, alternative sites can be just as dangerous. Sites like Tumblr quickly become echo chambers and a race to the bottom. They've been very helpful in providing a space, but the lack of oversight makes them potentially dangerous.
To answer your question about your friend, bisexuals are often one of the least supported and understood demographic groups. This brings us back to my earlier point about echo chambers. It is common for subcommunities to gather around hate, and the LGBTQIA+ community is no exception. There are many spaces where otherwise queer people gather to denigrate bi identities, invalidating entire labels because they don't take the time to understand them properly. I would argue that there are also a number of people who do this to make themselves feel better. "Finally someone I punch down to". Even the queer articles and literature of the 70s were hostile to bi people.
This is one of the many reasons I think there needs to be better LGBTQIA+ spaces. Moderation is important, but so is free speech. It is a fine line to walk. But one thing that's sure is that 90's style "free for all" internet can be very harmful for kids.