What about going to a party? That is a purely social event without any hobby attached to it. Hell, you can find random parties to attend on Meetup or similar if you really wanted, which I've gone to.
0.) Daytime activity so you get sleep and don't have to drink.
1.) Regular membership - meeting same people over and over again so that friendship can happen after months.
2.) Regular time and place so it is easy to add to schedule, agree with partner on who has kids and so on.
3.) Good fallback for when you dont fit in initially. Common topic.
4.) Safety. It is safer then party with strangers.
5.) Excuse. People need excuse to socialize. Socializing is seen as waste of time or as being bad parent. The club gives excuse for why you are not lazy for doing it.
If you have hard time getting along with random people and you need time to open up and get confident with others that is really bad idea. I think book club where mostly the same people who are also less outgoing is better option.
> Monthly social book club, not too serious, new faces always welcome.
> Monthly book club exploring everything from X to Y with a focus on Z. Newcomers wanting a place to discuss how P Qs R with like-minded friends always welcome.
What is wrong with people wanting to go to that type of party?