[Nelson69]

You cannot write safe code in any Turing complete language? That's a bold assertion that I don't believe is true. Surely you can use formal methods to develop software and maybe even prove it's correctness and security, it's costly in multiple ways but the language of implementation doesn't prevent you from doing this. It is possible to write secure code.

If we replaced everything in C with Haskell, we'd have an entirely different problem. The attack surface wouldn't involve buffer overflows and stack smashing, it would involve various DoS attacks. Those might be easier to address though.