The problem is that the miners -- whose fraud is proven with a transaction -- have the responsibility of including this transaction in the chain they control. W

The problem is that the miners -- whose fraud is proven with a transaction -- have the responsibility of including this transaction in the chain they control. Which means the only solution is to fork: now we have two or more chains (any number of valid chains which includes this proof can exist) -- how do we reach consensus on which to follow? Before the fraud, the miners were allegedly responsible for reaching consensus. And when they commit fraud, it's assumed that the network can reach consensus without the miners (on a single, valid chain which includes the proof of miner fraud). If everyone except the miners were able to reach consensus on a single chain in the first place, why did we need the miners?