> If the programmer forgets to lock the mutex the system won't stop them from accessing the data anyways, and even then there's no actual link between the data being locked and the lock itself, we need to trust the programmers to both understand and respect the agreement. A risky prospect on both counts.

Not every language is like that. I would not use language (that allows this) for parallel programming. You can use other ways but how can you guarantee everyone who will edit the code-base will not use unenforced mutex?