I disagree.

If you gave the service away for free and allowed people to be anonymous, there would be no private data that needed managing. In the 90s, a major proportion of websites on the internet had forums like that, which people set up on a weekend (think phpBB). What the hosting provider charges is small change.

If you do charge, you suddenly have sensitive data to manage, either eating into your profit or creating a liability for you and taking away from people's privacy if you don't do it right. So much so, that it might even generate a loss at 50 bucks per year.