Re: Lily, Sev, Mary, dark magic
I forget who originally proposed this - probably whitehound or jodel - but someone theorized that the *original* use for Cruciatus was as a sort of quick-and-dirty battlefield spell to tell the living from the dead (and thus quickly identifying who needs help) by delivering a powerful jolt to the nervous system, and that the spell was later corrupted into something one has to want to cause *pain* with. So that's not exactly a non-harmful use for the present spell, but it does point to the possibility that even this spell had could have had a legitimate use once upon a time.