Do traffic lights protect the flow of traffic, or do they protect people? It seems reductive to fixate on traffic lights stopping intersecting flows of traffic, when the intent is to ultimately protect people from slamming into (and thus injuring/killing) each other. It may be a tempting counterpoint that traffic lights don't do anything to protect someone from cancer, heart attack, etc -- but that's simply out of the scope of the protection that traffic lights are intended to provide.
Similarly, it seems odd to me to suggest that a mutex protects code -- what is it protecting that code from? How can the code be corrupted, damaged, or otherwise harmed? A mutex does prevent other non-lock-holding threads from running simultaneously, but that's all in service of protecting the data. The data is protected by imposing order on the execution of the code -- by serializing access to that data.
Controlling something isn't the same as protecting that something. A traffic light controls traffic, but it protects the people sharing the road. A mutex controls the execution of code, but it protects data.