The framers of the Constitution felt so strongly on the need for the people to have the right to protect themselves from governmental tyranny, they put it second only to freedom of speech.  Whenever someone says "you don't need a <insert item name here>", that is when you need it most, because they are trying to protect their political power by removing yours!

CBS News correspondent has excellent primer here:

https://www.facebook.com/ColRobManess/videos/1181040665244700/