How the Purge button works

In The Cabin in the Woods movie the need for the Facility to have a purge button is unexplained. Given the ultimate consequences of its use, what is its logic?

(If you haven't seen this one before, you're doing yourself a disservice by not watching the real movie first. Go get it!)

Basing my opinion on that of an anonymous contributor to the Cabin wiki and what one can see on the theatrical release, I think that the elevator lobby was not meant to pour out the army of nightmares. The area can be described as a capital letter 'T' with the vertical line having the elevator doors with the guard booth at its bottom. On either side of the horizontal we have two exit doors  one leading to Administration  (the one towards the giant snake slithered away) and one to Engineering (from where the two security squads came from). Both these doors, along with that of the guard area look entirely unsuited to hold off anything, so one can safely assume that the Purge was not intended to be directed towards this lobby, but somewhere else, only resulting in what we saw in the movie to malfunction, quite possibly due to Marty's tampering with the wires to make the cubes run backwards. Or maybe to an oversight, for once Dana's and Marty's cube was located, it was directed to the lobby area for their retrieval, but so were the rest. This would also explain the small interval between activation and release.

So what for?

The Purge, judging by its name, was meant to get rid of everything on one go. Possibly, the creatures were not immortal in the sense in that they had an 'expiration' date and had to be renewed from time to time. Possibly then the current batch of creatures might get all tainted at once from 'something' as to make them unsuitable for the Ritual making it necessary to vacate their quarters  offseason for a new batch of nightmares (bred? captured?) from the Facility's departments (Zoology a top candidate). The elevator lobby would be then the loading area and quite sensibly the the Purge button would be there and not in the main control room, which monitored the Ritual proper.

So where to?

Maybe a safe disposal place within the Facility where the creatures could be controlled and dealt with. Or as the  anonymous contributor said, to the surface. Maybe there, they would turn on themselves saving the trouble to exterminate each one, or they would just die off by themselves (daylight? their expiration date?) . Releasing them all to ensure the Ritual's completion seems like an overkill, but maybe still an option.

Defeating the true Scotsman

It seems to me that there are four ways of beating the True Scotsman self-sealing argument. This fallacy is notable for being impervious to counterexamples; once one is given, one of its components is redefined by the other party to hold his ground. Still, this gives us enough of a foothold to pry a way in.

Symbolically the Scotsman's argument can be presented as:

~∃x(Sx˄Cx)

Read as "There is no Scotsman who does a Crime like that" or  alternatively "All Scotsmen refrain from committing such crimes".  Let's stick with the first reading. Once a counterexample is offered the patriotic Scotsman might reject it by redefining Cx (The chap is a Scotsman but what he did is no crime) or Sx (That's a crime all right but he is not a True Scotsman).

Overall, informal fallacies are best dealt with by bring them out to the open and exposing them by explaining why they are so. A first way then to beat the true Scotsman is to highlight that the argument at hand is a known fallacy and then offering Flew's prime example. This should suffice for most cases, since addressing the self-sealing argument by name shines light squarely on it and the absurdity of its general form adds close to decisive weight to your side.

One can go further in, for the sake of exposition, or to win over the skeptics,  by  directing  attention to the change of definition on which the fallacy hinges to a wider or narrower scope which in any case is different from the intended common use.

Secondly, we can can highlight that no counterexample is possible under the self-sealing strategy which makes the argument a no-go. Whatever is thrown at it can be conveniently redefined away.

Thirdly, this can be further clarified by offering a patently True assertion such as  "There are no triangular circles"  and showing that it even that could allow a counterexample by drawing a figure, showing how to reproduce it or writing down the appropriate equations, while the self-sealing argument offers no such courtesy. Furthermore, one can ask the patriotic Scotsman to offer a counterexample of his own and watch him squirm (though I think this one can backfire as one is more likely to receive a blank stare in return).

Lastly, the best defense is to settle & agree on the definitions before embarking on any discussion. This is especially true when dealing with a known or suspected weasel. One can still act midway by asking what he means by this or that term: "What do you mean by Scotsman?" Ask him to be thorough. Once he or she commits he or she  cannot go back without losing face. Of course it helps having impartial witnesses that can attest to the facts or the ridiculousness of the explanations resorted to by the Scotsman.

More examples of self-sealing arguments that follow the same general form can be found in Critical Thinking: Consider the Verdict (4th) by Waller