the point isn't that it's impossible to write C that's safe, it's that doing so requires 100% success rate of a human implementing something correctly. furthermore, the main cases where C can get a performance benefit over safer languages are where there is a complicated invariant that ensures safety. the problem is that these are incredibly easy to break during refactoring, or when a different dev modifies the code later. compilers are much better then humans at verifying that code is correct.