They most certainly DO NOT cost anyone anything.
The prime message of all third parties is that there is no difference between the two major parties. That is their whole game. They say over and over their is not a dimes worth of difference between the Democrats and Republicans.
What studies have shown is that all third parties are the same. If the third party has a candidate they vote for the third party candidate. If the third party does not have a candidate a lot of them don't vote at all. And the remainder split their votes between the two parties. If the Libertarians don't have a candidate about half of them will teach the Repubicans a LESSON by voting for the Democrat and the remainder will vote for the Republican.
Splinter parties are of zero value to either party.
Look at the Greens. People would think that every Green would prefer (earth in the balance) Gore to Bush. But 2.8 Greens voted for Nader to teach Gore a lesson. But if Nader had not run 1.4 million Greens would have voted for Bush to teach Gore a lesson and the rest would have voted for Gore.
They would not have changed the outcome at all.
The Libertarians try to fool the Republicans all the time. But they fool no one in the party. They don't help and they don't hurt. The are completely a non factor in every race.
Good. Now that thats settled, we can stop with the libertarian bashing and get back on post and to the Onion and it's socialism bashing.
You may, of course, continue to believe that if you wish, even in the face of convincing evidence to the contrary. The best case is the Senate race in Georgia in 1992, in which neither major party candidate got a victory (they were virtually tied, and the Libertarian pulled three percent. In the runoff, the Libertarian candidate endorsed the Republican, who then won by a 51%-49% margin.
Now, I don't like many things the Libertarian party does (especially their ostrich-like foreign policy), and it is amateurishly run. But to claim they have no effect on close races is to fly in the face of the facts. You may believe that attracting the libertarian votes would cause a drop in moderate votes attracted, and that may be true, but I think it's debatable.
If the Libertarians don't have a candidate about half of them will teach the Repubicans a LESSON by voting for the Democrat and the remainder will vote for the Republican.
In my experience this is flat-out wrong, and I challenge you to find any hard data to support it. I hang around with quite a few LP party members. If they have no LP candidate, they choose Republican over Democrat by at least a 2-1 margin (the same margin the Georgia Senate race suggested, by the way.)