Incredible suggestions here, truly. Yes, let's aspire to be Haiti - a literal failed state. Gangs control something like 60% of their capital city, and citizens who have taken the law into their own hands before have ended up getting burned in their houses as retribution by the gangs. And how exactly does the deterrent effect of public executions work on a shooter who walks into a public place with zero intention of leaving there alive, as was the case in the last several major mass shootings?
It's unrealistic at this point to ban guns, there's simply too many of them in this country and too many people who would never comply, not to mention there are legitimate purposes for them. I personally don't think that even needs to be the solution and is often just a straw-man to get people worked up; in many of these cases (though not all), a simple increased minimum age or restrictions on purchase would have sufficed. What I definitely don't think is the solution is reducing barriers to purchasing or carrying a gun, which several states either have enacted or are in the process of enacting. Florida's recent bill removing the need for conceal carry permits is particularly funny in the wake of two fatal shootings and something like 70 guns confiscated during the always nightmarish Miami Beach spring break season. What do they figure is going to happen next year? I'm a gun owner myself, and probably every other time I've been to the range some dingus does something completely idiotic that makes it clear they do not know how to responsibly handle a firearm. Does anyone actually feel safer knowing these sorts of people can now conceal carry everywhere?
From a policy perspective, our society has made the decision that having guns around generally outweighs not having them around. Or at least, some people decided that a couple hundred years ago and for a variety of reasons it's basically stuck. So instead of having crazy people run around with knives (and killing basically nobody), our crazy people run around with assault rifles in elementary schools. Pro gun people - the kind with maximally or even just very expansive views of gun rights - can hem and haw and act sad or outraged about mass shootings, but that's essentially the bargain they've made.