But what they can do with 51%? Not much.
They can omit transactions from the blocks and they can go back some blocks and double spend transactions sent to them. That's the extent of it. They can't spend my coins.
Wrong, wrong, wrong.
With 51% they can destroy bitcoin, they can happily stop bitcoin with that. They control everything. They can go back months in the blockchain, rewrite all that and yes, they CAN spend your coins, if your coins were mined in the blocks that they reverted.