Is Haskell or ML 100% secure and not prone to bugs? The original multi-sig wallet code did not contain the error. It was only when Parity refactored it did they introduce the error. Sure, it would have been nice had Solidity not defaulted functions to public, but the error was the fault of a human and not the language. That said, I agree with their recommendations that functions not default to public and the use of simple contracts encapsulating complex contracts.