I don't know if it's because of the two-party/first-past-the-post political system, or if that's a consequence as well, but everything about the US just oozes binary thinking (even on the international stage: remember Bush's "if you're not with us, you're against us" war rhetoric).
There's no room for nuance, everything must be black&white. The typical HN visitor should have the mental bandwidth for nuance, but more often than not that same mentality is showing even here.