The issue is that in real life you can talk one on one. With the internet you have go-betweens, moderators and all that which limit what you can say to each other more than the two parties themselves limit.

Of course the limited reach of the spoken word and inertia of the speaker put limits on how much shitposting you can do in meatspace, but sometimes it's still preferable to have as little moderation as possible and instead enable each user to filter outer the noise on their own.