51% isn't all powerful. It would mean you could chose what transactions to process and you could potentially (and very visibly) reverse transactions that happen while you have that much hashing power. That's it, you can't transfer money to you.

Merchants who worry about reversing transactions are advised to wait for a few hours before transferring the thing of value, this reduces the ability for someone to deploy a 51% attack and if they did, it would be pretty visible.