Bitcoin is fundamentally a voting system. That is the clever bit. Answering “Did A transfer his funds to B?” is a trivial piece of public-key cryptography. “Did A transfer his funds to B before attempting to transfer them to C?” is decided by vote. How is that not terrible???
Reason 1 is that it’s costly to vote. That has to be better than letting any scumbag vote for free. But not that much better.
Reason 2 is that you are then rewarded for voting, if and only if you voted for the winning side.
What that means is that there is a huge incentive to vote for what you believe to be true. Trying to vote against it is bound to fail, because everyone else has huge incentive to vote for it, and because it will cost you big money.
Forget the fashionable silliness of applying “blockchain” to every problem. Think about applying “give people incentives to get it right” to every problem. Think about making “non-human value maximisers” out of people.
Related: are secret ballots the worst thing you can do to a democracy?