The US is NOT the paragon of democracy.
In a two party system, the small extremists can't win enough seats to be of note. That's a feature, not a bug. As we have seen many times before in the US's history, small movements move up through the party primary process. So you have the best of both worlds: a lack of easy access to government by extremists and a path to changing one of the larger parties via the very democratic primary system.
I don't think the US system is perfect, but its good; it solves a lot of problems of governing very nicely. The framers did their homework. The idea that Euro-style parliamentary systems are unequivocal better is a questionable premise, especially since it did nothing to stop the rise of Nazism in Germany (or even protect the lives of the Jewish minority) and other lesser but significant social failures (Greece's white supremacist Golden Dawn winning 22 seats in parliament recently for example.)
Not to mention, the States are fairly autonomous by Euro standards, so the state level legislature/courts/constitution are actually important and not just the bureaucratic/administrative arm of the national government. That gives a lot more local representation than the generally top-down decrees of Euro states - and that's on top of whatever the hell the EU is and all of its trans-national top-down decrees.
When it comes to politics HN is conspiracy kiddie central. The US has a real two party system on top of dozens of state and local jurisdictions, all part of a larger checks and balance system. Sadly, I see a lot of criticism from Chinese and Russians who want to badly equate their broken autocratic system with our system, and that just isn't correct.