You can tell as much about people (and organizations) by looking at who their enemies are as you can by looking at who their friends are.

Watch the reaction of the anti second amendment advocates and politicians when the NRA is mentioned.
They get positively livid and start foaming at the mouth. To those who oppose 2nd amendment freedoms, the NRA is public enemy #1.
That alone tells me that the NRA is worthy of my support.

I've been a member for over 30 years, and just signed my 17 year old up as a member as well.