My response would be that while it's true that clearnet forums have more reach than darknet forums, there is a risk that pushing people away into really isolated corners radicalizes them even more. If you have a really big open discussion platform, maybe you get assholes saying that Texas should secede or making racist statements, but you probably also have some amount of normalization from regular right-leaning folks who disagree with that. However, if you ban some political opinions, maybe you end up with isolated islands with fewer people that hold much more extreme views, and nobody to tell them that they are going off the rails and pull them back to reality.