> ...but the moment you ban/deplatform/censor/etc... then they begin to form isolated groups with no counter-balance of rationality.

The first such group that comes to mind is Heaven's Gate, which I think illustrates the opposite:

A brief reading of Wikipedia suggests to me that key members arrived in place via media attention, even though they spent significant other effort trying to recruit members.

https://en.wikipedia.org/wiki/Heaven's_Gate_(religious_group...