I think part of the problem in the US is the two-party system that you have. It means that many people (in both parties) don't really fit at all neatly. Way up north where I live, we have another, decidedly socialist party that those on the far left of Nancy Pelosi are welcomed into. They're called the "New Democratic Party." They never get to form a government, but the Liberal part that DOES often form government in Canada (the majority of the time since the beginning of the 20th century), is free of them, and thus can be more effective centrist in the party platform. And we've had another new party (People's Party of Canada) split off from the Conservatives, much further to the right. They probably won't win any seats in the House, or if they do, they'll still be marginal. But again, it allows the remaining Conservative party to speak to the more solidly central and sensible conservative members of society.
And it allows, if they can get elected anywhere, for those voices on the fringes to at least be heard, without too badly interfering with the more centrist parties' agendas. All in all, not a bad thing, really.