Decent human beings couldn't or wouldn't do the things the Headmaster was required to do -- ergo, he couldn't be decent.
This fic, written for the 2012 Deeply Horrible fest on LiveJournal, is a painful and masterful exploration of the lengths Severus has to go to to survive both physically and psychologically (as long as he must). It's the literary equivalent of one of those extreme close-ups that makes one unconsciously draw back in one's seat in the movie theater. The reader gets to go along for the ride as Snape methodically de-humanizes himself for the sake of the Greater Good.
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