I don't really have anything against third parties, in fact, should American democracy ever see some much needed structural changes they may in fact become useful and effective parts of our system and government. As of right now, they ain't. My entire lifetime has seen a slew of highly principled egoists that changed the system all for naught, excepting of course if you think Clinton/Bush owes their presidencies to Perot/Nader. There's been no significant third party growth as far as I can tell, at least to the point where they can do anything but prop up people who have no friggin chance of doing what they say they want to do. My first Presidental vote was for Nader, if you had told me 16 years later the Green Party would be no better off then it was now I'd probably go back and pull that lever for Gore (hey, I was in a solid red state, he wasn't winning anyway).
Its enough to make a guy cynical, but I have in fact seen a highly successful and very transformative political movement in my lifetime. The Tea Party has been so very good at effecting change, and within a relatively short window of time also, a very vocal and passionate minority was able to seize the reins of a entrenched party and successfully battle not only their own party but the opposing one as well and has been hugely successful in many ways in passing their agenda.
That their agenda is a nihilist, intellectually disingenuous con-job on their constituents and the country at large doesn't really matter. They've been able to push local, state, and federal governments far to the right with surprising efficacy.
Third parties will never matter in this country until we get some very solid election/campaign reform, guess which party supports that now? If people want to continue wasting their time on their lost cause so they can feel better about themselves, fine, okay, sure buddy, knock yourself out. Your actually working counter to your own interest, real and rapid change can happen, but it won't happen without engaging with the entrenched system that's already in place.