The way I look at it, If there are more than two parties with a credible chance to rule, the stakes are not high enough for voters to sort themselves by the rule, "No fucking way should those idiots be in power." That said, there should always be a radical (but not credible) 3rd party (or 1st party faction) around to both drain the real nutjobs off of the dominant parties and spur people to be reasonable in a smart way rather than a lazy way.
That's been the problem in the U.S. since the 60s. Both the Communist Party and the increasingly separatist Blue Dogs spurred the adults into making serious changes. From then through about 2005, the Nixo-Reagian wasteland of secret rule and quashing of radicals created two ruling parties competing to find the dumbest, most inoffensive way to gain political donations and time on Meet the Press.
I hope it remains difficult to quash radicals (on the Internet) for the future. The nutjobs need to identify their dumbness to the community and the dissenters need a way to develop their ideas. Without the web the gatekeepers have too much power to cull intelligence and independence out of the political herd.