Political Polarization

Why are there liberals and conservatives? Why are there two main parties? Why does everyone (even though they may not admit it) find themselves leaning towards one side or the other?

One of the greatest lines from Thomas Jefferson’s Declaration of Independence is where he states that we all have the right to life, liberty, and the pursuit of happiness. This basically means that we should be free to live our lives and pursue our individual path to happiness.

What gives one side the right to define the stance of the other side by taking an extreme position and claiming that anyone who disagrees believes the opposite extreme?