What is it really?

I often talk about the sunsets, or my flowers, or my family, but this topic is a little different.
I've been noticing something this past year we're are back in the states.
I don't recall I noticed it so much when we left for overseas in 2002, but it has really been staring me in the face.
When people identify themselves in tv, or newsprint, or blogs, or internet, or in letters or in person I often hear several identifying adjectives.
They will say: "I'm a conservative, I'm a liberal, I'm a right-wing evangelical Christian, I'm a Democrat, I'm a Republican....and on and on.
I think what sticks out the most to me when I hear "I'm a right-evangelical Christian", as if a more liberal or non evangelical approach in their religion doesn't make a Christian a Christian.
It's the labels I'm having a really really hard time with.
When did Americans become so polarized. When did we have to identify ourselves in such a dividing way?Do we only want to socialize with or be friends with those who think exactly like us? Do we feel so insecure we have to identify ourselves with labels?
As time goes by it feels more and more divisive to me.

Maybe it's because it's an election year and I've not been around in an election year since 2000.
It's feeling more and more alienating to me and I'd love to hear people's take on why we as a nation, people, religions, political parties feel we have to talk the person we are communicating with into our way of thinking?
What has happened to the melting pot we have always prided ourselves in being?
What about not always thinking our way is the only way?
I find it all shocking and surprising as to what has happened to the many peoples and groups who are yelling at us to change our way of thinking.