The strongest argument is to support a sort of poor man's const-generics. Consider a function like strchr(). This locates a character in a (const) string, and r

The strongest argument is to support a sort of poor man's const-generics. Consider a function like strchr(). This locates a character in a (const) string, and returns a (non-const) pointer to it. The idea is that you can use this on both const and non-const strings. Call it on a const string, you get back a non-const pointer (which you better treat as const!) But call it on a non-const string, you get back a non-const pointer, with which you can mutate the string. So a single function serves both const and non-const uses. If casting away const-ness were disallowed, the compiler might conclude that strchr()'s returned value cannot alias the input string, and its optimizations would defeat this design. Anyways that's the original rationale.