Quote Originally Posted by RdMarquis View Post
Perhaps she's just not willing to believe in an effect neither she, nor any unicorn she has never met has produced? The only pony to use magic for an explicitly evil purpose is Nightmare Moon, after all.
I don't feel that intent (good or bad) has to be part of the picture.

If definitions are the problem, here's my take on magic vs. curses:

Magic is whatever unicorns do. Its exact nature, limits and so on are apparently known, at least to some degree, by the inhabitants of Equestria, but not to us in the real world. For our purposes, however, it can do anything the writers decide it can do, so effectively it can do anything we can imagine. The only real limit we need to care about is that only unicorns can do it. This may be proven wrong later, but we assume that the ponies of Equestria believe this, whether or not it's true.

A "curse" is something magic-like done without magic, something that can not be explained by magic, most likely because the one doing it isn't a unicorn. Other terms might fit this definition (I can't think of any right now), and "curse" is just one example of this. You could say "curse" is an example of something "supermagical" (as in supernatural).