You could do a hard-fork and slash their stake. In PoW, you can't do this.
> With PoW, an entity could theoretically out mine the 51% attacker
Not in the case of "selfish mining attack", where you may never know that an attack is happening until it's too late, you'll have little chance in defending with hashpower since the attackers will have a significant head start...
So ... theft?
you're being intellectually dishonest or even outright manipulative here.
there were never 184 billion coins created on bitcoin chain, there was a bug in validation logic of bitcoin client that made it follow the chain that was invalid.
are you seriously trying to compare that to stealing coins from somebody on a valid chain?
really?
They're not stealing coins from someone on a valid chain, they are forking away to another chain and slashing the user's stake. The user will still have all their coins on "their" chain and it's up to everyone else to decide which chain is "the right one". If the 51% user is truly malicious, the majority of network participants will move away to the new chain, rendering the 51% user's tokens (near) worthless.
so being successful is punished by destroying all wealth of the richest participant in the network? nice.
> If the 51% user is truly malicious
Having 51% doesn't automatically make you a malicious user. People also wouldn't move away to another chain simply because someone or some group owns 51%. They would move if said person or group abuses the power they get from owning a majority.