Right now, I am not a member, and do not plan to become one (but anything can change), due to this reasoning: a good percentage of people that are in my life are moderate to anti-gun. In fact, long before I was a gun owner myself, I use to tout the same kind of anti-gun, anti-NRA things that these people say. If I joined the NRA, and they found out about it, I feel that I would lose influence with them. What I mean is, if I'm trying to convince these people why it's a good idea to own guns and fight for your 2A rights, and if it comes up that I'm an NRA member, I imagine most of them would dismiss my reasoning at this point with "Oh, well, of course you'd say that...you're in the NRA!"
I think I can make more of a difference out there by
not being an NRA member, because then I no longer fit the stereotype that these people (family, friends, students, neighbors) have already dismissed. It's also the same reason I don't subscribe to Guns & Ammo, wear Glock T-shirts, etc. I want to maintain the tactical element of surprise.

So, this is not at all to say the NRA is bad, or I don't support them. I definitely support them. But in my situation, I believe the best way to make an impact is from a more covert position.
Example:
Friend: So you went and bought a gun, huh?
Me: Yup, I sure did.
Friend: Didja join the NRA too? Haha!
Me: The NRA? No man, who do you think I am...some kinda gun nut?! I just want to protect my family. There's a lot of bad people out there. Don't you think?
Friend: Hmmm, no doubt.
Me: So why don't you get a gun, too?