The standard complaint is the opposite. In a generic first past the post two party system you should end up with two barely distinguishable centrist parties.

The standard complaint is the opposite. In a generic first past the post two party system you should end up with two barely distinguishable centrist parties. https://en.wikipedia.org/wiki/Hotelling%27s_law https://en.wikipedia.org/wiki/Hotelling%27s_law But the US system is far from generic. Instead it has several tweaks that make it tend towards extremism. The primary system is probably the biggest factor.