Interesting conversations online have gone the way of the Dodo Bird. Many platforms need to be advertiser friendly, you need lots of moderation to get onto the app stores, and if somehow an interesting places does spring up eventually one of the big players finds a way to take it down.
That’s half the problem. The other half the problem is that if you do manage to create a really open platform it will be destroyed by bad faith actors and trolls. These will drive away the good stuff and turn your platform into some kind of echo chamber or worse a hate and psychosis ridden hole like what the chans became. The bad chases away the good.
Deep substantive discourse requires good faith argument not propaganda techniques, straw men, and trolling. It also requires maturity.
> it will be destroyed by bad faith actors and trolls
Popper's paradox of tolerance plays out every day on social media. If you take a strong free-speech no-moderation approach, your forum will sooner or later be destroyed by propagandists and trolls. If you try stronger moderation, you might keep those at bay but you also lose many of the true free thinkers so the creeps still win.
Jerks have an innate advantage on the internet, which makes conversations "across the divide" almost impossible; those are best left for RL environments where trust and physical presence can keep those impulses from manifesting. The best one can do online is choose which side of any relevant divide you're going to be on and limit participation to those who share some core beliefs. (Comparisons to women's colleges and HBCUs should come naturally at this point.) Sometimes this allows interesting (if somewhat bland) discussions. Other times it just leads to ever more tightly defined factions - e.g. genuine socialists vs. social democrats - turning on each other.
I've been actively involved in online discussions for 40 years, and I was even a moderator on a political forum through millions of posts. I wish that experience had left me with better solutions, but sadly I have to report that it hasn't. "Leave the sensitive stuff to RL" seems to be the only real answer, with "reduce use/prominence of social media" as a corollary.
