"The reason to stick with the GOP is that it is the best avenue to get conservative voices in government. Yes, there are a lot of Republicans who aren't conservatives. But if conservatives don't have the votes within the Republican party to nominate and elect a conservative, then by what logic can they get the votes among voters at large? It's a lot easier to win a primary than a general election."
This is the great flaw in our system. It is winner-take-all, with no room for proportionality. It kills third-parties much as the shade from an old, decrepit tree prevents new growth from sprouting. In fact, any third-party would be, in reality, a "second" party, since our much-vaunted two party system is, in reality, a one-party system (call it "Republicrat" or "Demopublican") with a right and left wing. The best way to remedy this is the one that would never happen; a European-style unicameral legislature; a way that might work might be instant-runoff voting, but the Republicrats which run state elections would never let that happen.
Why are third parties such a great idea? I mean, does it really make a difference whether a candidate runs as a member of the Constitution party or the Republican Party if its the same guy with the same views? You'd still end up with the same spectrum of people in Congress -- just different party labels. Ron Paul is a pretty good example there. Does he vote any differently now than he did before?