Sadly that seems to be the case on most issues, not just gun related issues.
Critical thinking is out of fashion. People come to "know" what they think they "know" because "someone said" and they happen to agree with that someone and/or regard that someone as some sort of authority.
It has little or nothing to do with actual experience, logic, or any other form of validation other than "a lot of people believe it so it must be true". That's the echo chamber you describe and none of them have any clue they are perpetuating an ad populum logical fallacy.
On the flip side, if they disagree with that someone, rather than let that challenge their own thinking and belief(s) and then seek to validate what they think they know through empirical evidence, testing, etc, they just ignore it. That's the closed mindedness you mention.
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Most people today are also pretty poor when it comes to qualifying statements - identifying when they are applicable and when they are not.
For example someone will insist that carrying a full size automatic with a capacity of 15 + 1 to 18+1 rounds along with 2 spare magazines is important for concealed carry. The basis for this argument is either "that's what law enforcement officers carry" or the related "I might encounter multiple assailants", which is just a variant of the LEO argument.
LEOs might need that high capacity and two spare mags because they go looking for trouble in dark places and/or serve warrants or otherwise get into situations that might involve multiple assailants.
Armed citizens, at least armed citizens with brains and any degree of situational awareness do not.
Recognizing the qualifications around a statement of fact is important in setting priorities and finding a balanced response to a problem.
For example, I have a CZ SP101 tactical with 18 round magazines and it's great for tactical shooting. But it is large and heavy. With 2 spare magazines it's really heavy and if I had to carry it all day long in concealed carry, sooner or later I just wouldn't. It would do me zero good in the truck or on the dresser when I was inside the local stab and grab getting the wife ice cream at midnight.
In contrast, the pistol by itself isn't bad, but a CZ 75 PCR is better - lighter, smaller, but still very controllable and it still carries 14+1 - for concealed carry purposes. And when concealment really matters the CZ 2075 is a lot smaller and lighter, yet still easy to shoot well and it still has 10+1 capacity.
In the winter or in the woods where I value more penetration a S&W 686+ is a good choice, even though it "only" holds 7 rounds.
In short, I'm not looking for "what LEOs carry", or even what I used to carry as an LEO. Instead I'm looking for the best balance in meeting my perceived needs across a spectrum of comfort, concealment, effectiveness and my ability to shoot it well.
Shooters don't achieve that just listening to some guy talk about what is "best".
