I've never understood the logic behind Republicans of the 20th century [2]. AFAICT, they think the 2nd gives them "the right to defend ourselves from a tyrannical government". That's clearly bullshit. First, because what constitutes tyranny changes a lot from person to person, and only legislation can define it clearly and "democratically". Second, because the former means you're legitimizing political violence in a democracy, precisely the system where that kind of shit should not be allowed. So in fact you're just making terrorism, or at least the kinds of terrorism you like, legal, with all the contradictions that would bring. Timothy-McVeigh-like bullshit ensues.
[1] Of course, back then they were considered to be respectable persons that followed the law.
[2] They're not the only ones, of course (cf. Black Panthers, which I personally am more sympathetic to, since IMO there was clearly oppression there), but they're the loudest.