The key difference is that there are invariants you can rely on as a user of the library, and they'll be enforced by the compiler outside the unsafe blocks. The

The key difference is that there are invariants you can rely on as a user of the library, and they'll be enforced by the compiler outside the unsafe blocks. The corresponding C invariants mostly aren't enforced by the compiler. Worse, many C programmers will actively argue that some amount of undefined behavior is "fine".