Just think, less than a handful of elections ago, the election was, in part, determined by a few dozen people deciding to vote Libertarian in Florida. How different would the world be today if they had decided the lesser of two evils was Gore?
Reality: our system of government pretty much means there are always going to be two major parties, not three. That's the way it works.
There is no convincing the third party voters they are living a delusion. There are usually more than two parties on a ballot but there are only two parties that have any chance of being elected president.