I am not sure if all liberals think they are more enlightened than conservatives, but whether they think so or no, it is a fact of life. Increased knowledge and intelligence tends to produce people who are more open minded, accepting of others, and not afraid to say so. Most intelligent and enlightened people tend to discard their old religious views as superstition and rather barbaric in nature.
Man has the capacity to rationalize and in most instances ascertain what is possible, what is real, and what is plausible, and differentiate them from those that are fairy tale in nature, and illogical, and simply designed to instill fear and guilt in people as a means of control over them.
Conservatives on the other hand seem to fear progression, cling to old unfounded ideas and rituals, and display (or at least say they do) a fear of punishment by their vengeful Creators.
People with the least amount of education, knowledge, and/or intelligence tend to be more religious and fearful of the unknown, and therefore want to remain in the state they are in, in lieu of accepting greater challenges that make for a better future for all of humanity.