The Etheruem developers propose a change to invalidate the hacked Ethereum. If you do not agree with them, you do not have to run the hard fork.
Sure and the HF alt created when the chain splits will be exposed to regulatory threats and will need to hire a bunch of lawyers and at the same time undermine the trust in the network. What happens when the FBI knocks on the Ethereum foundations door and asks for another soft or HF to disable or freeze assets on a naughty smart contract? Great job guys!