Not disagreeing with your perspective at all, but there at least have been hidden enclaves on platforms like reddit that are not achievable on platforms like Twitter, in which consenting adults could find each other for consenting activities.
You can't do that stuff on Twitter or IG because everything is too out in the open. You can do it on some other websites but they don't have the userbase and broader appeal and legitimacy like reddit had.
Just not sure that there's a way to achieve it in the Fediverse because we're not just talking about the fact that there's a small but hopefully trustworthy group of admins who could wade through everyone's posts and DMs, or surely Google is indexing your comment and post submissions... We're talking about a solicitation of a sensitive nature goes out so much further than you can imagine.
Please know this is not about finding new channels to conduct illegal activity!