Why does it seem Republicans or Conservatives are so angry?

I’m fairly moderate and over the years have voted both sides of the fence. In the past 10+ years it seems that Republicans have claimed the “conservative” title and deem anyone (or anything) not “conservative” bad. What’s up with that? Why the exclusivity? What’s wrong with moderate thought? Why the vitriol?
I’m not Republican bashing or Anti-conservative. I’m just wondering why there seems to have been such a fundamental shift in the position(s) of the Republican party.
I tend to lean Democrat these days, as I don’t feel like I’m getting slapped down for my “liberal” opinions at every turn.
And, since I’m asking, why does the Republican party keep allowing Rush Limbaugh to be their spokes person? I’m hard pressed to think that he’s truely where the party wants to go.