In real finance, there is an understanding that technical loopholes can exist, since not every outcome can be foreseen when writing laws, but the legal system can frequently prosecute against a series of actions which are, individually, legal, but which together are taken in order to achieve something illegal.
That is, modern finance and the law also attempt to deal with intent.
But in the Ethereum smart contracts world isn't the whole premise that the code is the law? That we don't need any of these pesky courts or banks or auditors or anything: the code is the law, and the decentralized blockchain will enforce it.
With this worldview, if the attacker simply exploited poorly-written code to find a loophole, how do the owners of Index have a leg to stand on?