Let's say someone come up with a decentralized forum software where no authority can touch. That's pretty much what darkweb is. Every type of filth will leak from a place like that. Let's face it, decentralization is not always the perfect solution. It is because we are trying to solve the wrong problem. The problem isn't the forum software we use. We are the problem. By "we" I mean everybody. It is because we can't stand to live in a perfect world.

Just like how the Architect described it in the movie, the Matrix.

He created a world where everything is not perfect, everybody is not happy and only then his simulation worked to some degree. Every other perfect world simulation failed instantly. We can't be happy if everybody's happy. We are feeding on other people's misery. That's also the reason why capitalism prevailed.