If anyone needs convincing that people should be required to pass a simple background check before purchasing a deadly weapon, they should look no further than Jumanji, the classic 1995 film about the worst board game ever.
Now, obviously, this particular firearm purveyor happened to be pretty corrupt. But, thanks to the background check system, the vast majority of law-abiding gun dealers not susceptible to bribes with rare coinage would have discovered that Van Pelt hailed from an alternate jungle universe and was therefore ineligible to purchase his Daewoo USAS-12, which he proceeded to fire with reckless abandon in the streets and department stores of small-town New Hampshire.
Under our current system, this very same homicidal jungle hunter from another dimension would, after being prevented from buying his weapon at a gun shop, be able to stroll over to a gun show, or a computer, and buy it there without anyone ever checking whether he's allowed to own it. If you think that makes sense, you probably work for the NRA.