Formal verification and a manifesto or constitution. When you have that combination the developers have a reputation and must conform to expectations based on their own pledges or promises in their own constitution or social consensus. If you're talking about formal verification then you can prove what is impossible behavior for that particular smart contract.

The DAO had neither of these and was rushed out on a platform which wasn't ready for that kind of money. Myself and others warned before the hack that this was going to be possible but without the necessary clout it was just a bunch of "amateurs" in the minds of the experts working for Ethereum.

Of course now it's changing, you see formal verification of smart contracts as the norm and immutability is no longer considered some sort of ideological necessity. But it's not all the way there yet.