> In this paradigm, the blockchain becomes the single public source of truth/database for everyone's content.

Which blockchain? There's scores of public blockchains.

As for infrastructure, are you high? Blockchains are shared among miners, they're not going to carry massive amounts of data. If you try to decentralized storage like IPFS then you have to maintain infrastructure to have data actually available.

If you try monetizing every social media transaction you'll have no users. No one is going to pay money to post a picture of their breakfast or to change their profile picture.