As far as the constitution, it is unclear if a type of armament is unconstitutional. Certainly, the government has the power to regulate.
Having said that, the above is only an interpretation of writing. Most hard core gun owners would agree guns should be legal, but they wouldn't want their neighbors carrying a bazooka.
You're missing the fact that anything (organization or individual) survives in the U.S. by what they can produce, either by product or service for benefit. The NRA provides a service to gun owners to protect their right and is faithful to that service. This, in itself, doesn't make the NRA bad.
You must understand that the government of the United States is a referee. To maintain a balance someone has to watch the playing field. It's the government's job to make sure neither liberal nor conservative thought has control, unless it is the will of the people.
Are conservatives more vocal than liberals? Is that why you hear more conservative language? It depends on the state you live. If you want an accurate gauge of what people think, look at local ballot questions, here is the truth of the local population. Many talk, but few are up to the moment.
Edit: Point in fact, sit in any Boston bar and you will hear reams of conservative conversation. We are a conservative state, yet we vote liberal in big elections.