The programming model is not quite the same. You can get away with some things if you know only one thread is running at a time. You have to mutex a lot less for one.
I disagree. You don't know where in your code the scheduler will interrupt you, it could be any time, so if you do unsafe things to shared structures you still need the mutex, it's just less likely that you will get rescheduled at precisely the right moment to hit it.
In other words data races will still potentially cause another thread to see a data structure in an intermediate state. It will just be a rare bug instead of a potentially more common one.
