It's a private forum. I certainly hope the owners can control its content. If they think it's in the best interest of their service to display pornography, by all means. However, I will state my preference unremorsefully whether they happen to value it or not.

To address your statement for what it is -- a fallacy -- I will give you a firm no. I prefer individuals owning themselves along with their forum servers.

If people want to block people from posting pornography on their property, that should be their right.