At least where I've voted in the US, there are rarely only two viable choices for a state or national legislature position. Some states resolve this using primaries for D/R candidates, and a few use stricter runoffs where there are frequently several D/R candidates. At least in the towns where I've lived, there were noticeable policy differences between many of these candidates within each party, although I will readily admit that I doubt this holds for most of the US. Also, it's still generally not as widely varying in views as in countries with 3+ parties (if made viable through proportional or similar voting) instead of the multiple rounds system popular in the US.

Going back to the original point someone made in this thread, I think this two-party multiple-views system in the US actually helps a bit to drive polarization. Seemingly disparate views are drawn together under a banner of [party] with an obvious (not actually clear or cohesive) enemy in the [other party].