You're half right. It's best to consider all sides of an argument, however the people that believe that there are only two sides are generally considered idiots. The fact that there are only two major political parties is just a mathematical consequence of the election system, not a reflection of the population's actual beliefs.
It's not just a mathematical artifact though. Political affiliation has deep cultural significance in the US. It permeates every aspect of a person's life and affects all of their relationships. There are plenty of Americans who will demand to know what you think of the president, on first meeting you, and then decide whether or not they like you based on the answer to that single question.
You don't see this in countries with many political parties that each grab only a small piece of the pie.
> There are plenty of Americans who will demand to know what you think of the president, on first meeting you, and then decide whether or not they like you based on the answer to that single question.
There are plenty of americans who will form their opinion of you based on which sports team you like, as well.
I think your observation is not so much one of politics permeating all aspects as it is that our current culture is superficially tribalistic in nature, with many tribal signifiers being used.
> There are plenty of Americans who will demand to know what you think of the president, on first meeting you, and then decide whether or not they like you based on the answer to that single question.
This is a relatively new phenomenon that will hopefully not be around for long.
You can see this throughout the culture, from the legal system, to robust support for free speech, to the quite frankly Christian morality (a belief that there is original sin in the body politic that must be atoned for) that permeates even the most hardcore progressive, atheistic left.
[1] https://en.wikipedia.org/wiki/Dualistic_cosmology