I was once advised never to discuss this topic with Americans because it’s impossible to have a normal logic discussion… But I’m a bit dumb so I’ll do it anyway! (Assuming you’re American, sorry if I’m mistaken!)
A couple of points:
You’re right, I’ve never actually seen a bulletproof vest in real life. Notice that your laser focus on the technicality of some vests is very interesting and explains why they are not very common. Yet it doesn’t really implies that it couldn’t work. For example, the slim-fit c’est you’re taking about would be an excellent solution to give a chance to run away. In a similar vein, ABS brakes on a car do not perfectly prevent collisions but still help reduce the severity of accidents.
Regarding your imaginary scenario, please re-read the thread… It seems to me that you’re the first one mentioning the “very frightening scenario”. I’ll skip this one for now since it’s a different topic.
In public, would a concealable vest be good enough against concealable guns? Would a concealable gun be effective against a non-concealable big gun? It seems to me that all your arguments against vests also applies to guns…
Replacing guns by non-lethal tools would probably be just as effective to disable an attacker, while at the same time being a good first step to detox from this gun addiction, hopefully leading to a reduced number of gun accidents.