Why are a normally sane populous like those of the USA so stupid as to endorse the policies of the NRA ?

Obviously because your initial assumption that a populous like those of the USA are normally same is false. The American population is letting its definition of sanity be determined by biased media outlets, who are more committed to promoting a particular political party than to reporting the truth. Consequently, the current populous of the USA is exercising about as much sanity as the populous of Germany in the late 1920's and early 1930's. Our logic has been subplanted by media-defined "common sense" instead.

So what do you have to say about the people who were first disarmed, and then murdered by their own governments, in countries like USSR, Germany, Cambodia, China, etc.

56 Million disarmed people murdered by their own governments over the last 100 years.

Hard to give you and your question ANY credibility after your asinine attack of the NRA.

"Why are a normally sane populous like those of the USA..."

Have you ever been here?

Americans sane? Haha, you've got to be kidding.

We're a pretty stupid place.