There are two services (one built by me) out there which have this in mind, providing an online space for deep public discussions around a topic.

Taaalk (https://taaalk.co/) is mine. It is currently less focused around debate, and more around exploring topics:

E.g. OCD: https://taaalk.co/t/exploring-obsessive-compulsive-disorder Eating disorders: https://taaalk.co/t/discussing-eating-disorders Bitcoin: https://taaalk.co/t/bitcoin-maxima-other-crypto-things Flag design: https://taaalk.co/t/the-power-and-significance-of-flags Chess: https://taaalk.co/t/how-to-think-about-chess Psychedelics & Mental Health: https://taaalk.co/t/falling-inward-discussing-the-role-of-ps...

Etc...

Another alternative that is built by a fellow HNer is Debubble (https://debubble.me/). It is more focused around debate than Taaalk. There are a fixed number of messages / discussion.