That last point made really drives it all home. You can't keep guns away from people, period. I used to make shotguns for fun with $40 and a trip to the Home Depot plumbing department. I currently own a 3D printer and a roll of Taulman Alloy 910. I could make one mean, bitchin' AR-15 lower receiver with that stuff, and have it fully assembled and ready to fire in under 24 hours' time. Guns are some of the simplest machines on this earth, in basic principle. Any old asshole with some tools can get the job done if shit gets so spicy that they couldn't get one from the store.
The "but criminals who are motivated enough will find a way to kill" mindset seems to be ignoring the issue at hand, in which, yes, creating stricter laws in regards to the access of guns won't solve mass murders entirely, but it certainly is much harder to kill with a knife than it is with a gun.
By saying this you are implying two things. One, that criminals even use the legal means to acquire a gun in the fucking first place, which is just about the most retarded thing I have ever heard, considering that any murder committed with the gun would more or less have a paper trail leading right back to the murderer, aaaaaaaaaaand... Two, that legal gun owners are the ones committing anywhere near the bulk of firearm deaths. It's frankly statistically insignificant (we're talking like >2% here), and I don't think it's worth punishing the law-abiding citizen who actually went through the trouble of doing things the right way. If anything, the fact that someone did all of the work to get their thing should tell you that they're probably not a school shooter. Most school shooters would just be content buying whatever works from their local MS-13 chapter.
Fact is, if they can't get a gun legally, it's easy as piss to get one illegally, and no regulation can fix that aside from having a government security camera in every home. Furthermore, if they can't get one even illegally, they can simply build one. You literally cannot stop it from happening. That's not defeatism, it's just my acknowledging that the world is not a vacuum where things just work if the plan sounds good enough on paper. Unless you have the time, resources, governmental overreach, and manpower to have every square inch of the United States on CCTV, you're never going to stop it.
So at that point in the pattern of logic, you have a choice. Either you lock the country down to the point where everyone's living in fear of the all-seeing government, as seen in the Combloc countries of Eastern Europe, or you leave things alone. Realistically speaking, Gun Control is at a permanent impasse at this point. If any more legislation is made against the Second Amendment, you're either going to see a revolt, or an absolutely ridiculous power-boost for the government. 2A can't be damaged any more than it has been in places like California, without the concept of a constitutional right to bear arms being an unfunny joke.
People cry about "oh well we need criminal background checks for people wanting to buy guns". Well, guess what, you already have that in about 99% of cases. I don't understand why people think we don't have that. Private sale is another matter entirely, and I think that with the private exchange of things like standard rifles, Curio and Relic Firearms, and muzzleloaders, it shouldn't matter at all, anyway. Every state with a handgun registry still requires the government to step in on private sales of those, too. You still have to fill out the ATF form, you still have to get the background check, and you still have to wait a just fucking absurd amount of time before you can own your gun.