They are not many multitudes in the US. Good on you, but my experience is that most people stick with one group and regurgitate the party lines. I think this comes mostly from very polarized TV shows.
Likewise, if you disagree with them, they instantly assume that you are with the other group. It is strange.
The two-party system easily evokes the ancient knee-jerk reflexes. The millennia-old "us against them" tends to eschew any nuance and instill the war mentality. Either you are "one of us", and subscribe to the bulk of "our" views, or you are "one of them", and are assumed to subscribe to the bulk of "their" views.
Likewise, if you disagree with them, they instantly assume that you are with the other group. It is strange.