To answer the original question and with the benefit of eyes born outside the USA and having travelled widely, including across the USA:
Culture varies widely even within fairly small nations, indeed it tends to vary a lot even within each state (think about it in your home states) but often people are blind to shared cultural 'givens' until confronted by a place which does it differently.
A few examples from my own experiences:
Syrup and sweet pancakes next to meat, for breakfast. What?! This was utterly weird to me when I first met it.
In Switzerland they don't care what guns you have in your car but the exhaust emissions better be within the legislated range and the engine better not be too noisy, both are grounds for on the spot fines; the loaded guns on your backseat are not.
Buying alcohol on credit? Weird. This is illegal where I hail from, though the usual fudge is to have a meal as well, run up the entire bill and then settle with a card.
Children driving cars? Wow! In many nations you must be an adult, with voting rights and all that jazz, in order to be given a driving licence.
So... back to the USA.
In Arizona I was utterly unfazed by people carry guns around me, although it wasn't very common within the cities and large towns, however I had gone there with knowledge of its gun laws and where I was born we are fed a rather distorted image of the USA's gun laws anyway, so a lot of us expect every American to be wearing a pistol and cowboy boots. ;¬)
In New York I don't think I ever saw anyone with a gun, even many people who were ostensibly police officers didn't appear to be carrying (openly at any rate).
I was surprised to find that Texas doesn't permit openly carrying a firearm (I have since read up on the laws and understand the historical context) because we usually imagine it to be even more full of people with pistols, hats and cowboy boots. :¬)
The bottom line is that people are often ignorant of differences in laws even within their own nation, if their local experiences are different from what prevails elsewhere.
I remember some people in an international chatroom getting very angry and upset and shouting about the FBI (as if they have international jurisdiction!) because a 16 yo was openly talking about being in a sexual relationship. This was (and is), of course, completely legal where she lived (UK) and at various times and under various circumstances was / is legal even within the USA.
There is a common misconception, fueled by the "sex crime" obsessed media, that the age of consent is 18 everywhere in the US. In fact, in a majority of states it is 16 or 17.
In Virginia (an 18 state), if you are 18 you can marry somebody aged 17 with parental consent, but sleep with her beforehand and you will be charged as a felony rapist even if she consented because she is a "child." However, marry the "child" and it's OK. What?
In the end, it is just an arbitrary line like all other age limits and says nothing about whether the person is mature or not. Unfortunately due to Puritan heritage and influence of the "bible belt" Americans have a tendency to be rather infantile and prudish on some issues.
The other day I was watching one of those operating room shows (I flipped to it by chance) and they were showing a caesarian section. There is no problem in the US with showing all manner of blood and gore spilling out onto the table but you BETTER NOT show the vagina. Then when they got the baby out, they censored her privates also.
I mean, it's a BABY. Maybe I'm not a real American, or maybe I'm a pervert, because I find nothing at all lewd about a nude baby. But yes, let's please see more of that bloody, sliced n' diced subcutaneous fat spilling out.
Most Americans have never seen foreign TV so they don't understand. In Europe it's the opposite. You can see topless women in daytime TV commercials, but the amount of senseless violence and gore shown on American TV is rare. I think the Europeans have it right on this one.
A German friend once asked me "Why do you Americans not let anybody walk down the street with a beer in his hand, but you can walk down the street with a gun?" (It's the other way around in Germany.) I had to admit he had a point. The best answer I could come up with was "I guess Americans are incapable of drinking or acting responsibly so we have to carry guns to protect ourselves from all the other irresponsible Americans."
There is a lot of stubborn ignorance and immaturity in this country, and not just due to "liberals" but also due to conservatives (see above examples). Fortunately, personal liberty is an American cultural difference I happen to agree with. It is the one truly unique and redeeming characteristic of this country, and it makes life here worth living. Without it I wouldn't be able to put up with so many ignorant and irresponsible people. I just hope they can't breed enough in my lifetime to take my rights away.