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One of television’s great contributions is that it brought murder back into the home, where it belongs. - Alfred Hitchcock

Ladies and gentlemen, let's make one thing very, very, very clear. Murder is bad. Murder is immoral. Murder is not acceptable in any way, shape, or form. Murder is among the most heinous crimes a human being can commit, and should not be taken lightly.

Unless, of course, your victim is a Mary Sue. A fictional Mary Sue. It's still not good to kill real-life ones—every sentient creature has the right to life. It's a good thing Mary Sues probably aren't sentient creatures (or, if they were once, they aren't now or they won't be soon). What they are, exactly, is unknown; but based on their behavior, they could be natural phenomena that create continuum-destroying plotholes, the result of a disease of some sort which can assimilate its victims, repeated incarnations of an eldritch abomination, or the artificially created and programmed creatures manufactured at a Mary Sue Factory or written by a Suethor.

Killing Mary Sues, whatever else it may be, is necessary; and many Sues are murderers themselves, usually through indirect Suefluence. See, many Suethors have a habit of getting the significant others of their Lust Objects brutally murdered, just so they can "be there" for said Lust Object—that is, get in his pants (effectively, committing rape through mind control). Murder also tends to be a staple of Disturbing Acts of Violence fics, obviously.

The PPC may kill Sues, but there's a clause in the whole murder thing that lets PPC agents dispatch Mary Sues with extreme prejudice: it's like war, except the Mary Sues don't know it (Except for the factory Sues, who do know what's going on). Mary Sue, if left unopposed, will eventually destroy her entire continuum (and all the sentient creatures in it). Therefore, she must be destroyed.