Plus, I think this image of a lonely new fan walking into a con looking to make friends is largely some kind of rescue fantasy.

My experience, inside and outside of the fan community, is that people generally only enter a new social situation in the secure company of existing friends.

People start coming to cons as a group, basically.

Maybe that's starting to change as cons become the venue for online meetups - but even people doing that are meeting with an existing community or group of friends. The only real issue for them is finding them.