Forums, social media... these stuff needs to be centralized.
Centralization is not always a bad thing.
Agree. Some things are not designed to be truly decentralized after all. A good example of this is the Internet. We cannot decentralized the web, by storing all the world's data in a Blockchain ledger. The decentralized nature of Blockchain, makes it impossible to scale towards millions of users worldwide. Either you scale indefinitely while sacrificing decentralization, or all the other way around it. The Internet needs massive scalability in order to function as intended. Which is why, the idea of implementing a social network within a Blockchain seems to be like a bad one in my opinion.
The immutability of the Blockchain ledger, will prevent transactions from being reverted at will. Imagine if someone posts something illegal or offensive, without the ability to erase it from existence. This will turn into a disaster for the underlying Blockchain ledger, turning into its demise within the long term. The attempts of Steem and Voice to revolutionize social media, might turn to become a failure in the future. It's yet to be proven whenever Blockchain could fulfill many of the tasks performed in daily life. As far as I know, there are some areas which Blockchain works flawlessly (like Finance and Smart Contracts), while in others, it's terrible (like social media, and even, Bitcoin SV's metanet).
Nonetheless, Blockchain-based social media such as Steem, AKASHA, and Voice have some interesting proposals to take the world by storm. However, it's unlikely they'll reach the same level of adoption as traditional services (like Facebook and Twitter) because they're more of the same. Innovation is key, in order to attract users into Blockchain-based social media platforms. Just my thoughts