Am I unAmerican to say I will vote 3rd Party vs. Two Corrupt Parties married to global corporate interests?

Until we pass campaign reform, and Instant Run-Off Voting, all we get is Republicrats from these two parties each offers a version of corporatism with different rhetoric same result. Why continue to let our taxes be looted for corporate gain, by both parties vs. reject them both? Seems to me supporting new parties and Instant-Run Off Voting, which yield a majority winner, is the only way to stop the charade, and the downward slide of the USA. Voting for the best worst seem a losing proposition.