Hi JKS,
It's not common that you and I disagree on these things, but here I'm going to come out against the characterisation of these methods… let's take it bit by bit.
For some reason, I've been looking at or seeing posts and videos of disarming techniques, either for knives or guns. I've got a simple question: Why does just about every disarm assume that the person with the weapon is an idiot?
Honestly, I don't know that they do… there can be major disconnects in understanding the behaviour of the aggressor, which is a bit different, but the way you're describing the armed assailant as an "idiot" doesn't quite match to my mind. And I have a feeling it might be because of differing perspectives and expectations… which gets towards some of my previous comments about training against "trained" not guaranteeing, or even being that transferable to, success against "untrained".
For example... A simple gun disarm begins with a gun shoved into your back. You pivot, trap the gun, and do harm unto the attacker. Another, gun to the front... Raise your hands, move into the assailant slowly until you suddenly move in and take the gun, etc. Knife disarms often assume that the attacker is going to be stupid, and advertise the knife from a range where they loose the advantage. (Note, please, that I'm not even getting into the legal consequences due to shooting/stabbing/whatevering someone after you've disarmed them…
Well, let's take it back a step then… what are the students actually defending against here? Just because there's a weapon involved doesn't limit it to a single type of encounter.
Let's be real: I take you down at gun point, I'm not 3 feet away. I MAY be 6 or 10... but, y'know... my Glock 22 reaches out a hell of a lot further and hell of a lot faster than you can run, so I'm probably going to try to have 15, 20, 30 feet or more.
Sure… but, and this is important, who are you and what is your background (obviously, JKS, I know who you are and what your background is, this is simply making a point that you're not the same person as the assailant in these scenarios)?
If I'm going to stab you... You ain't gonna know there's a knife until you're bleeding in most circumstances.
Which takes us back to what is actually being defended against.
Going off the top of my head; I haven't done any research into it yet -- but off the top of my head, most robberies with a gun do occur inside of maybe 10 feet -- but also often involve a barrier, or an implied weapon, not a displayed gun.
That would depend on the type of robbery… a store/building/bank, yeah… a mugging? Less likely to have the barrier there.
So... Why the hell do so many disarms assume that the attacker is an idiot, and gives up that range, advertises the weapon...
Okay, let's get to it then.
I'm actually teaching pistol defence (essentially disarms) at present, and they're not too dissimilar to what you're describing… and, really, I rail against the idea of "idiot" attackers pretty constantly (that's gotten me in some trouble with certain persons, actually…

. Within some Koryu, it's basically a creed of reality ("Teki wa baka dewanai"… "The enemy isn't a fool"). As a result, I look for realism in everything I do… within the context of the technique itself. So what's the context here? As I mentioned earlier, just because a gun is present, it doesn't make all the encounters the same contextually. If a gun is employed in fairly close range, the most common context is either a mugging or a hostage situation. Why is it that close? Because control is required over the target (hostage), and you need to be close to take what you need from the victim (mugging). In both cases, being shot is not the initial aim for producing the gun in the first place… which does allow for the disarms to be employed, as well as setting up what you're referring to as "idiot" attacks. Same thing with a knife, really… if it's drawn and shown, it's about intimidation, not damage.
When you describe the way you'd employ a firearm, the tactic and context is rather different… as an LEO, you're wanting to either gain compliance or end a violent situation with (potentially) lethal force. You're also trained in the employment of firearms in these contexts, which gives you a particular form of decision making and chosen actions. You employ your firearm in a tactical method… with an idea of the aim you have (which is different to the mugger), and a usage of distance that is congruent with that tactical approach. The knife assault you describe is not particularly "Law Enforcement" (ha!), but it is an ambush assault… which is different to the mugging/hostage/intimidation usage of a blade. Our use of a blade is very much the same… and, for the record, we do have knife defences designed to deal with such an attack as well… but then again, I'm not training people to be muggers...
So, why do so many disarms have an attacker in very close range? Because hostage/mugging style assaults are the types that lend themselves to disarming tactics… ranged employment of firearms (random shootings, drive-by's, mass rampages with assault weapons) don't lend themselves to such tactics. Knives, well, they have to be employed in reach of the victim, so having it brandished from a distance doesn't make any sense… and an ambush assault, although the response might end with some form of disarm, has (by necessity) a different beginning tactic/response. Are the attackers "idiots" for giving these forms of attacks? Nope. It's just one of the myriad that could be encountered. And, I might suggest, these are more likely (depending on where you are, of course) to be experienced by most of society than a random assassination attempt.
With all that said, of course, there are a range of things that can be seen in many of these training methods that do warrant the phrase "idiot(ic)" at times…