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Anyone could roll forward all the transactions again, so you need to do more than just roll back. You need to declare the transactions invalid somehow.

And unless every participant is in on it, you will end up with two cryptocurrencies afterwards. Holdings won't match on both chains. Find an exchange that is not running the same chain as you and spend a transaction that is valid on his chain but not the other, and by transferring out other cryptos you could empty their wallet.

The majority of participants do not in a crypto-currency.

Only the majority of the hashing power.

If a majority of participants rejected blocks that were on a chain that did not rollback the erroneous transaction, then the hash power would be forced to follow.

I believe the term for who decides is the "economic majority".

Hashing power can not roll back transactions. Hashing power alone can not change rules embedded in the software.

Proof of work is used to order transactions in the global ledger to avoid the double spending problem.

They did in Ethereum after the DAO got hacked.