How to stop the Purge

I think the problem with that is that not everyone wants to stop the government, most people are just out to kill out of frustration, some are just out to make money (as seen). So anyone out doing something non violent is just putting themselves in danger. Also, if insurance doesn't cover any damages caused during those 12 hours (which I imagine they don't, otherwise they'd go bankrupt), then you can easily cause enough monetary damage by just smashing the windows in those big offices etc.

The big problem with the purge is the thinking that one night of murder and meyhem would make all the other days crime free (as said in the first movie). In fact this would raise crime as people would turn bloodthirsty to the nth degree.

Very insightful suggestions by the original poster. Persuading public opinion to favor any extreme ideas, however, relies more on emotional arguments appealing to hysteria and frustration than on logic (I'm sure the 2016 presidential election results offer more than sufficient evidence of that).

I'd go with animal cruelty. Public opinion would quickly turn against the purge the minute the media started reporting abuses against animals, especially cute and cuddly ones. Protected from prosecution for 12 hours, I'm sure loads of people would not only take out their frustration on animals, but live-cast videos of their deeds, which would be a field day for the media for months afterwards. The politically correct middle and upper classes would feel much greater pity for animals than for the poor, the non-whites and the other human groups that are at their most vulnerable during the Purge, and since those upper classes carry more clout (both economically and in terms of voter turnout), loud objections would multiply quickly, pressuring politicians to change the laws.

(Which is not to say it'd cause a complete repeal of the Purge legislation – they might just tweak it to extend the same exemptions that high-level politicians already enjoy in the reality of the films).

Whatever you think about the films, I think the premise of the franchise is fascinating, and gives you great food for thought about real world issues, by comparison with the extreme fictional scenarios of the movies. I'd be particularly intrigued to see how other kinds of crime would fare during the purge, not only violent ones. For example, how many illegal immigrants would enter the USA in those twelve hours? How much snuff and child pornography would be recorded, and watched? How many business transactions and sales of anything imaginable would take place, free from consumer rights legislation and health and safety regulations?