Summary: Is there a fundamental human nature, or is it malleable? This is a key difference between the left and the right. The right takes humanity as a given, and tries to create a structure that accommodates man as he is. The left has a vision for a better society and tries to tweak man to fit in. Conservatives are willing to tolerate equality, so long as it doesn't get in the way of freedom, but liberals are willing to tolerate freedom so long as it doesn't get in the way of equality.
