Dennis Prager is a joy to read: a talk show host and commentator who isn't afraid to use philosophical moral reasoning to convince us of his worldview. In his latest column--The Case for Judeo-Christian Values, Part III [see the previous parts Parts 1 and 2]--he argues that "there are four primary problems with reason divorced from God as a guide to morality."
(1) Reason is amoral.
(2) We are incapable of morally functioning on the basis of reason alone.
(3) The belief in reason alone is itself based on an irrational belief -- that people are basically good.
(4) Even when reason does lead to a moral conclusion, it in no way compels acting on that conclusion.
Read the whole thing.