Many Americans have unusual (for us) attitudes to guns. It seems nonsensical to us (or even most Americans?), but when they hear about people getting shot many feel inclined to do something “to protect themselves”.
At one level they might actually have a point. Even if guns were banned tomorrow for the law abiding how long would it be before “bad guys” ran out of bullets?
They also fear a “slippery slope”. In many European countries they banned automatic weapons, then semi automatic, then a few years later pretty much all guns (as in the UK). Therefore they will defend AR-15s now, despite the cost, to avoid having to defend pistols in a few years.
For whoever said that it sounded like a heavy machine gun, that seems unlikely. It sounded like an ak47 or similar firing a 100 round magazine (first bursts seemed to last about 10 seconds).
I recall in the US they tried to ban large capacity magazines after some of the shootings a few years ago, but that fell through because it “wouldn’t make any difference”.
They say you live and learn, but many people don’t. So sad.