I think in the modern age especially in America the whole "we thought it was fireworks" thing doesn't really happen as much so it's weird shooters underutilise suppressors. It'd buy they much more time and cause less panic meaning the victims wouldn't react especially if they used sub-sonic ammo. As far as how shootings would've been different I guess shooters who where more methodical (Breivik, Cho, etc.) would've got much higher kill counts then shooters who just went in blazing (Eric and Dylan for example) It would've been extremely interesting if Paddock took the time to get suppressors for all his guns.
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Moral code, whuzzat?