>And despite the low murder rate, many are still convinced that they're about to be killed by one of those many, many guns
I suspect the reason is because a higher than average proportion of people who post here tend to live in cities (and be in their 20s), where crime is both naturally higher and vastly more visible than it is when not in a city; this is why city people tend to be a lot more authoritarian and risk-averse than people who live in regions with population densities with a more favorable ratio of People Who Destroy Society per mile.
These people are people who, all else being equal, do things the average person would rather them not do, like property crime, pounding the apartment walls at 1 AM, shitting in the street, and the like. It's possible to build places where these things don't happen, but none of them are compatible with maintaining the political power of the risk averse as they currently exist today (even though, ironically, those places give even more power to the risk-averse).
Case in point,
>Many are even required to carry transparent backpacks, just in case one has a gun.
which is only in effect in the places with most of the crime (read: inner city), and the occasional suburban district where irrational risk-aversity got a foothold. Everywhere else tends to be a little bit saner and would prefer to not constantly broadcast a message of "be constantly afraid of a thing that's vanishingly rare" (which is what the backpacks are meant to symbolize), at least until irrational risk-aversity starts paying political dividends in those areas as well (or it is forced upon them by the cities if the state isn't structured in a way to keep them in check).