It wouldn't get the guns that guy like this. He would still keep or find a way to get more guns. The drug cartels in Mexico would pop champagne in celebration that they could make gun running an even bigger part of their business.
We logically talk about how difficult it would be to deport 11 million undocumented immigrants across the US, now try to remove 350 million legal guns that can be stashed anywhere and left for years without anyone being wiser. It's impossible.
Besides the 2nd amendment ensures that will never happen.
Of course it's impossible, so what? The point isn't to get every gun ever.
The more guns you get off the market the higher the price for a gun on the black market would be, and while yes that'd also make it a more lucrative business, it'd also up the stakes dramatically because then those groups instead of just being another way someone can get a gun in this country would then be the only way someone gets a gun into this country I promise we could put more law enforcement onto them. I mean we also might not, I guess that'd be our decision, it's not a given, but seems to me if you lived in a hypothetical country where guns are now illegal and the only new source of weapons into the country each year are Mexican cartels and not thousands of gun shops across the country it seems logical to me that they'd get increased scrutiny from law enforcement.
I'd also throw out that a lot of this isn't going to happen in a vacuum. If our companies are a major exporter of weapons to Mexico to begin with I think we could, you know, exert a little control over those companies and get them to maybe not sell thousands of guns to Mexico to begin with? Maybe we wouldn't but, you know, we could. I'm not familiar with how many Mexican gun manufacturers there are, if any, but surely we could exercise our control over our own, right?
To me currently enforcing gun laws in the United States must seem pretty futile. You take shit off the streets that's legally sold down the block in pawn shops, supermarkets and sporting good stores. It must make actually focusing on the criminal importing element of that business seem, well, pointless. What's the point of heavily focusing and expending resources on a trade dwarfed by your own legal trade of the same items?
And public pressure would probably start getting pretty immense for the government to do something if this were the case. Can you imagine the blame laid at the government's feet if there were a gun ban in the United States and some big mass shootings happened from guns brought in from outside the country? Either we'd drop the ban and re-arm ourselves or they'd fucking commit some more resources to catching gun runners at that point.
I think the biggest issue would be how to avoid Ruby Ridge type stand offs and I say just wait until they die. Again the ban needn't be immediate, just gradually get them back. Stop allowing the manufacture and civilian sale of new guns now, slowly buy back those from citizens who want to commit now, make the standards of ownership for people grandfathered in annoying enough that many casuals will turn theirs in to save themselves the hassle of dealing with legal gun ownership, confiscate the ones you'd normally confiscate during routine police work and finally just make those grandfathered weapons to a person non-transferable and collect them up when that person dies.
In the meantime as guns get gradually rarer and rarer the street price for them should just continue to rise making their use in crimes rarer and rarer. And while this guy specifically could have probably bought guns illegally under a ban as he had enough money to probably circumvent any ban in any country, the question beyond financial ability still remains as to whether or not he could have done so while avoiding detection from law enforcement.
Because once the act of trying to buy large quantities of ammunition and guns becomes "strange behavior" in this country the mere act will start to draw attention from concerned coworkers, relatives, even legal shop owners, let alone the police and all the Federal entities. Think about that, how weird is it that buying that arsenal now doesn't even raise eyebrows? Of course in an environment like that where you can go in and buy body armor, and fucking semi-automatic battle rifles somebody buying those things doesn't raise much suspicion, but what happens once that's illegal? What happens when a guy walks in to a legal gun store(assuming something like bolt action rifles or levers or something survive a ban) and requests an M-16 and a shit load of rounds?
We live in an environment here where prevention is nearly impossible because merely seeking or having the means to do this in the first place is both entirely legal and not weird. So how could authorities truly track every Tom, Dick and Harry that buy weapons illegally and why would family and coworkers alert anyone when someone's breaking no law and even if they did to what end could the police do anything about it when it's all on the legal up and up? But change that environment, change our culture and all of a sudden Tom buying a bunch of guns is "alarming" to coworkers, friends and relatives, change that legal operating environment for the industry to one where gun shops don't sell such weaponry and it's highly illegal and all of a sudden why is this strange person trying to buy a bad ass semi-automatic rifle, tracer rounds and lots of magazines? The entire operating paradigm would change. Now law enforcement would have far less people to look into, once the attempted, or successful purchase of an arsenal like his would be illegal then they really could look into everyone. If his friends, coworkers, family was weirded out and called someone they'd take it seriously because that would no longer be normal legal behavior in this country and if you owned a gun shop and some weirdo wanted to buy that from you and you passed that info along to law enforcement they'd have more reason to follow up on that.
And sure, maybe in the end this guy still would have flown under the radar, somehow found the right illicit connections to purchase these weapons and carried out his massacre but I guarantee that a lot more wouldn't and that number would drop significantly in later generations.