Shirky has this exactly right. I voted third party once, in 2000, and once was quite enough for me.

If people want more choice in their presidents and federal office holders, the US Constitution will simply have to be amended. The two-party system is not the result of “tradition” or historical inertia, it’s the consequence of rational actors trying to maximize their influence in first-past-the-post winner-take-all elections. This system was specifically constructed, by the framers, to compel voters to choose from a bare minimum of “safe” choices, all choices carefully vetted and approved by the rich and influential. This is not corruption, this is the very design and essence of our system. The system seeks to obtain from the voters their consent; not their stipulation, support, love or moral approval.

Changing this is a very laudable goal but requires institutional reforms, not symbolic votes for people, like Jill Stein, who even many of her supporters concede would make a terrible president. Casting a vote so that a party can get more ballot access, or federal money, or can attend television debates is the very definition of throwing your vote away. These are baubles and meaningless trophies, they don’t change the actual dynamic or incentives of the parties or candidates.