I used to organize a meetup for Javascript programmers. It was more about sharing information than about debate, but I think there might be overlap with what you want. The format was a regular meeting schedule once a month where 2-3 people would give presentations to show off what they’ve been working on, teach how to use a new framework, or whatever they were interested in. So in a way it has handing out information from on high, but I think because we had different people each meeting sharing their perspective there was a good element of exchange of ideas between peers.

Now it turns out that people need lots of leadership energy to create room for exchange of ideas. At the beginning I’d get about 6 people at each meeting, few of whom volunteered to step up in front of the group. So what I did was to show up every month, and talked about whatever topic I could come up with. At most of the meetings it was just me talking. When I did get other people to present it was through prodding and hassling. But people were interested enough in the material, and found enough value in just being in the same room with other people with similar interests that people kept coming back. It stayed small like that, growing slowly for maybe 2 years. But then we hit a critical point where there were enough people coming, and people were inspired enough that suddenly we were getting 30-50 people each month, and I had no problem finding volunteers to present. And it wasn’t the same volunteers either - we had a good rotation of different people interested in sharing their ideas. That continued for another 6 years before I moved and passed organizer responsibility over to the next generation.

My point is that a club like this needs a lot of energy and attention. It’s going to grow slowly. But it will grow if you keep at it, and put in the work. We reached that point where the group became sort of self sufficient in that I didn’t need to be the one making presentations anymore, and I didn’t need to actively seek out volunteers to present. But I still had to put in the work to make sure we had the meeting space available every month, show up to let people in, work out the meeting schedule, get food. Anything like this will die if there isn’t someone holding it together through force of will. But it’s worth it! It was a great experience!

I know you said you want your club to self-manage. But people need structure. If you ask people to show up and have stimulating discussion they’re going stand around awkwardly not knowing what to talk about. Something like a presentation followed by discussion gives structure that helps people to open up, and explore their own thoughts. Or since you want multiple perspectives maybe a debate or a panel format would work better for you. Get 2 or more volunteers to talk about a specific topic. I highly recommend lining up panelists ahead of time - you’ll have a rough time getting volunteers on the spot. If you prep your debaters ahead of time by asking them to present different views they might be less likely to simply agree with each other. Once your scheduled panelists get ideas flowing it will be easier to encourage attendees to step up to speak. You might have a debate or panel followed by open discussion, or rotating panel seats that people can step up to and leave as they feel inspired. But again, based on my experience I suggest being ready to be the one person standing up and debating yourself for maybe many meetings before the club finds a self-organizing energy.