Can "reason" be considered a moral absolute?

Most certainly not. Reason has never been sufficient to formulate an absolute moral law. First of all, when we think of reason, we must ask the question, whose reason are we referring to? Secondly, if it is your reason, is your reason absolute? In order for a moral law to exist, it must be given by a higher standard; a standard that is immutable. Certainly, our reasoning, even our rationality changes daily, for our ideas are daily confronted with others. In a changing world, only One Being is capable of establishing such moral absolute- namely God Himself.