Interestingly, this happened not to a blockchain, but to a protocol: https://www.coindesk.com/steem-will-hard-fork-in-just-hours-...

Justin Sun planned to take over steem, what did the community do? Fork it, and remove his power.

What gives things legitimacy socially is our perception that things are legimiate. On blockchains, one could argue the majority can more easily take away abusive power.