I disagree with that. I think if society in general push's and enforces certain types of laws it could be effective in reducing gun violence in general and mass shooting's probably to a lesser extent. Something like I outlined would just take time to do this since nothing ever happens immediately when you are trying to force behavior changes on a large segment of the population. 99 percent of gun owners are responsible, and probably would be for something like this because they know that it should be expected of them in the first place. While those who don't follow the law will eventually have to replace some part on there gun, show up with it not being registered or try to purchase it without registration of the type of weapon its for and then have there guns confiscated because they can't follow a simple law. The way it would work is that if you owned a gun prior to mandatory registration, you are not required to register it until you HAVE to replace a component on the gun. Then it is required when you try and purchase that component that the gun its for be registered. Failing to do so will instantly result in forfeiture of all firearms and charges being brought. If found guilty you won't get your guns back and you will no longer have the right to own any firearms for a set amount of time and your guns will be sold for scrap. Now yes guns will be out there, they will exist and people will still die to gun violence, but it will steadily decline because it reinforces certain types of behavior so it will happen less and less in general because its habit forming. And also the mental health aspect will take guns out of the hands of people who never ever should have owned them in the first place. It might take a decade or two for it to be effective because of the absurd amount of guns in the country but it will work because once guns are tracked, it will be harder and harder to purchase them on the black market because of parts requirement to keep them operational and the risks involved in not following the law will cause a tightening in that market to push those the costs higher.