Purpose of the "Purge All" button in Cabin in the Woods

As per The Cabin in the Woods Wikia:

The System Purge, also called just the Purge or the Carnage, was when Marty Mikalski and Dana Polk unleashed all the monsters in the glass rooms into The Facility. This was accomplished with a button in the control panel marked "System Purge." During the Purge, each and every one of The Facilities monsters are let out in waves, eight at a time. The first wave of monsters includes: the werewolf, the zombies, a witch, the Dismemberment Goblins, the dragonbat, the Giant Snake, the Angry Molesting Tree and the killer robot.

Why the facility had the need for a System Purge is unknown, but it is likely that this is a reference to the eleventh-hour deus ex machina that is a common trope in the horror genre.

So the button is an obvious satire of the eleventh-hour "deus ex machina" in horror movies. (Reference)

The only thing that I can think of is that this is designed to purge - i.e. destroy or remove all the 'nightmares' in the complex. It would have to be used in conjunction with whatever you needed to kill everything, poison gas or whatever supernatural 'thing' you need to do the job.

That said, you would need to have this 'agent' available, plus to leave the 'big red button' active seems rather careless. Any decent engineer would design failsafe mechanisms to prevent the button being used by unauthorized people, and in the event that it was to destroy everything, you would want it to only be active when the 'agent' was being used too.

Just as the ritual is rigged against the kids (they're forced into playing archetypal roles and making fatal decisions via drugs and subliminals), it's rigged against the facility workers. I think the button only exists for a survivor to push; if they make it that far, they must choose between self-sacrifice or self-interest (which dooms humanity). When the facility worker observes Dana on the monitor and says he's almost rooting for her, I think he has this outcome in mind. The gods need blood -- whether they get a little at a time or all at once is up to us.

I suspected that it stood as the absolute last ditch effort to kill the victims. Everyone in that facility knew their job, and that the youth must die at all costs. If all else fails, release EVERY BAD THING EVER, and hope for the best. Clean up crew can come by later to fix it up if there is still a world to fix.

I don't believe that's supposed to serve any real purpose, rather, It's a nod to all the monster movies where the hero comes across some abruptly added plot device that gives the victims a chance against the impossible odds. like when in a movie the victims find out that water or the common cold is deadly for the monster. What I want to know is: if the kids were going up to a cabin for the weekend, why the heck would they take an RV?