* If both chains are around equally popular full nodes will be fully aware that there is a fork and can send security warnings. Merchants who run a simple node and have only limited connections can double check on sites like blockchain.info (which should alert a big red security warning while there is a fork)
By golly, you've independently discovered distributed consensus!
This is somewhat similar to how Ripple operates. I agree that manual intervention is a much more prudent solution than the idiot-proof "longest chain wins." At some point, you have to give some credit to the user's intelligence.