Paid forums are niche area, it will not be a reddit alternative: the "filter" you describe is not geared towards maximum quality, but to enrich the owners of the site.

They have financial incentive to ban at the slightest provocation, restricting everything to safe and predictable "high-level dialogue" that can't challenge the status quo.

Reddit thrives on multiple levels of "dialogue" segregated into their own communities. Its pro-growth vs SA pro-elitist stance. Thats why SA will never be a reddit alternative.