The same argument could be made about an escrow account. Just because the account gets payed to one party by the third party doesn't mean that the second party couldn't sue the first for the money back. Assuming the third party made a mistake or (more in line with smart contracts) if the escrow was set up in a way were the pay out was just with relation to the escrow terms but wasn't in line with the contract terms between the 1st and 2nd party they'd be likely to get redress.

There's still a very real use for smart contracts in that you change what bad actors can do to act badly. Before they may have been able to breach a contract by ignoring invoices now they breach a contract by exploiting a smart contract loophole. Basically your shuffling the trust and risk around which can be a useful tool. i.e. it can be quite costly to enforce (and do due diligencece on) a contract with someone in another country so the cost and technical risk of setting up a smart contract may be much more preferable than the posisbility of having to legally enforce redress for breach in a regular contract.