3rd Parties don't steal any votes AT ALL. To say so reflects not having actually read the political platforms to know HOW DIFFERENT the platforms are. A late 2011 Gallup poll of Americans' attitudes towards govt reported 17% expressed conservative views, 22% expressed libertarian views, 20% expressed communitarian views, 17% expressed centrist views, 24% expressed liberal views. Wikipedia's page on the 2008 U.S. Presidential race said that 5 political parties HAD THE CAPACITY to have gotten the required number of electoral votes to have secured a win of the White House. They were the Constitution Party, Democrat Party, Green Party, Libertarian Party, and the Republican Party.
Clearly these stats and many others, plus the facts of the political platforms of the various political parties and of the candidates for poliitical parties 100% dispells the myth that 3rd parties are just fringe elements that only serve to steal votes from Democrats and Republicans. Democrats and Republicans haven't represented the majority view of the United States in decades. Problems 3rd parties get into are the lack of info the general public has about them being out there, being closer to their particular views, and the wrecklessness of people who choose to vote for what they believe is a winning horse rather than to vote what they actually believe in, plus obviously the issue of Super Pacs in our day that quite a few 3rd parties abhor as Unamerican, against the intent of the Founders, not in keeping with either a true Republic or a true Democracy, etc., etc.