Twilight Sparkle is a master of all things magical. This is a fact that nopony would argue with, and would be understood to mean "All legal and good things magical." This is not necessarily the case, after all, one must understand the forbidden arts in order to find, and stop their abuse.
What happens, then, when a threat that she cannot face herself comes to Ponyville? She must use that ancient last resort, damning her in the eyes of the law and the average pony. Making her an abomination to all the unicorns that don't understand or care about her reasons, and thus, making her exile or executed.

The credit for the concept goes completely to Rated Ponystar

Credit for the cover goes to DennyButt