That's the point though...they'll never get elected if people continue to vote for either of their percieved evils, with your logic that voting for any other candidate is pointless and letting it happen. That's ignoring the point in voting: deciding how things are run in the future. The biggest reason that voting for a third-party candidate is that the more people who do it, the greater the odds that more people will see them as viable in future elections. It's either that or get all the candidates into the debates, which is not going to happen as long as the media has their stranglehold.
Doesn't matter to me one way or the other, since I actually like who I voted for.