I got a membership card and packet from NAGR a while ago after never having signed up. I'm pretty sure, though, that the mailing list was purchased from conservative sources. I tracked similarly formated letters from NAGR to Michelle Bachmann. Now I never signed up for anything with her, but her mailers and emails were similarly formatted to an offshoot of a Ron Paul aligned PAC. I donated to Ron Paul's campaign before the NE primary in 2012 and my info has been bought and sold through the channels.
It is true that being more aggressive and setting their memes in a rhetorical pathos setting allows NAGR to snag a youthful and energetic following on social media. They are really modeled after some of the liberal social media sites in how they frame issues so pointedly and skewed buffering themselves from any rebuttal.
Now, if only they wouldn't create so much infighting!?