This is touched on in the later (and shockingly good) Purge movies
Purge Anarchy (2) touches on the idea of post-purge killing being a massive sin (but planning to rape and murder your tenants is perfectly fine...). And the ending radio narration makes it sound like paramedics, firefighters, and cops swarm en masse the moment the siren goes off (whether the cops would do anything is a different question...).
Purge Election Year (3) takes this a step farther with the addition of vigilantes. The idea of anti-purge militia is built upon from the previous two movies, but there is also the idea of "former gangbangers" riding shotgun on ambulances to help victims during purge night itself (with the implication of being the first responders the moment the alarm goes off)
But The Forever Purge (5) is actually set the day after the purge and depicts exactly that: What if people just kept killing? And it very much indicates that cops patrol and are ready to intervene and arrest any (south american women and black dudes) who look like they are continuing to purge.
The first movie is some right proper dogshit that is mostly a horror movie for middle class white liberals who think they are progressive but are just as ready to buy an assault rifle and "protect themselves". But 2-4 are increasingly good and focus more on what "purge night" would actually do to a world and acknowledges that it would be minorities that are predominantly targeted and preyed upon. And Frank Grillo (ironically) playing "what if The Punisher wasn't a racist shitbag and actually helped people?", Bubba taking a break from making shrimp to save Totally Not Hilary Clinton, and Marisa Tomei as a scientist? And Y'lan Noel as basically "Black Solid Snake murdering the fuck out of some klansmen"? Masterworks all. And The Forever Purge intentionally breaks the format but also modernized it in a way that was desperately needed. I like to compare it to Godzilla 2014 in that it didn't really work but tried some REALLY interesting stuff.
I saw the god awful original one when it came out and hated it. Then years later I was in a hotel room flipping around and saw a black kid running through the streets as some old grannies are throwing explosive baby dolls at him and was mesmerized. Watched the rest of the movies a few weeks later and am now a big fan. Although, I hear the tv show was somehow even worse than the original so...
I appreciate your writeup, but I'm curious as to what interesting things Godzilla 2014 tried, because I just watched that and came away thinking it had nothibg redeeming in the story or script (though the producions values were great)