What happens when an error happens and the site whipes your wallet? As long as the user agreed the contract you can do nothing to prevent this.
Usually, no one would accept such a contract ofc, but what if such a rule is "hidden" or masked by a more complex rule?
I am sure a lot of us wouldnt read the contract in detail and just accept it to get a little bit more convinience.
I am thinking of a smart contract in which everything is verified and eventually implemented using the blockchain. In which case, the gambling site would have no access to your wallet and cannot possibly commit an error wiping your wallet clear up to the last satoshi. There would be no third parties in this case because everything is to be facilitated by the contract in the blockchain.