I believe it's not desirable to criticize existing Web 2.0 platforms when discussing decentralized social networks based on distributed protocols. It's precisely because of the centralized nature of existing social networks that the idea of decentralization emerged. We should pay respect to the foundation created by Web 2.0 and look forward to the near future.
@omi_geek not entirely true. The web used to be open and decentralised (email, RSS, open and standard protocols like IRC, etc, etc) then existing social media platforms invented walled gardens. Nevertheless, I agree that it isn't desirable to discuss them. They are best relegated to the mists of time and used only as a reminder of how bad things got so we can steer away from it in the future.