There's no sin in voting third party, especially if one lives in a non-important jurisdiction. It's not equivalent of voting for the Republican/Democrat, etc. etc.
The only difference in opinion for people who say that is, what they really mean is that a vote is not an endorsement of the person you are voting for, but rather an expression of a preference for B instead of A. So if I vote for B, it doesn't necessarily mean that B offers me anything I consider worthwhile, only that I think the scenario of B winning would be better than A winning. Voting for C is me choosing not to contribute to the decision of the question, and I do lose my right to complain. But it's not the same as voting A either.
I reject the premise that the choice is only between A and B. The only people who have no right to complain are a the ones who simply don't vote at all.
Unless you are actively campaigning for Choice C or Choice C has a legitimate shot, you might as well not vote at all than support Choice C. You're basically voting Present.
