You're not 'assigned' anything at birth. You are documented based on what is or isn't between your legs. Really pretty simple, been doing it for 1000's of years now.
There are plenty of liberal and moderate posts here. They just don't make it to the front page because the upvoters following this stream are mostly conservative. Just like the election. :) I suggest scrolling the "NEW" posts if you want to see liberal and moderate memes.