only one party believes that an unborn human has rights and protections under the law regardless of whether or not the respective mother wants them.

only one party believes that two adults in love can be married under the law regardless of whether or not the respective people are of the same sex.

if nothing else just those two diametric positions seem to indicate an important and meaningful distinction between the two parties.

Even such an obvious litmus test as this is imperfect.

According to polling data, over 20% of Republicans self-identify as pro-choice and 34% of Democrats as pro-life.

There are plenty of Republicans who support gay rights. In fact did you know that the end of Don't Ask, Don't Tell stems from a lawsuit about the matter filed by gay Republicans? Yes, I know that Obama publicly takes all of the credit for that one, but the bill that he pushed for took effect on September 20, 2011 while Log Cabin Republicans v. United States forced an end to enforcement on July 6, 2011.

There is no simple litmus test. Each party is a coalition of people with enough common interests that they prefer one tent over the other.

Ever wonder if, in fact, those are not honest philosophical disagreements, but just rallying cries to divide the pool of supporters? See also: environmentalism, gun rights, etc.

Two teams play the exact same game on the exact same field. They wear different colors, but that's entirely superficial -- it has nothing at all to do with the game being played.

How can we demonstrate that this is different?

And another party entirely believes a woman should have the right to do what she wants with her body, and also that gays deserve the right to be married. They also believe in personal freedom and lower spending.

Yes, there are parties other than blue and red.

And to whomever says that a vote for a third party is a vote wasted -- congrats. You're one reason this country is in such a mess.

Only if you insist on applying the European spectrum to American politics. The thing to keep in mind, and this is absolutely critical, is that Europeans cannot vote in American elections. Therefore, the center of American politics, where practically all American politicians sit, is not in the same place as it is in Europe.