According to AmesG of RationalWiki:
In fact, if religion were the only source of morality, I think it would speak quite poorly for the human race as a whole, and demean the dignity inherent in humanity. Based on my personal knowledge of atheists, secular humanists, agnostics, etc., I have found that the areligious are often more moral than the allegedly quite religious. The precepts of the Ten Commandments are much more basic to human nature than some book, and the abandonment of the book that espouses the rules does not necessitate the abandonment of the morality that the book codifies!
But AmesG’s thin assertions are overshadowed by the deep analysis of R.J. Rushdoony:
If man alone speaks, and if man alone is the interpreter of life and reality, then man has no standard beyond himself. No attempt to establish a standard escapes the collapse into subjectivity and relativity.
Consider, for example, the approach to the Ten Commandments. A man born with an inheritance of Christian morality may drop the first four Commandments and insist on the humanistic validity of the latter six and feel this to be a sufficient and valid basis for life. The question can be immediately raised by one who calls the validity of the seventh commandment into question that humanistic fulfillment requires the abolition of this law, and only an outworn, guilt-ridden and masochistic psychology keeps men from unshackling themselves.
Every single commandment has at one time or another been dispensed with in some functioning and successful society, and the Christian interpretation too infrequently regarded. Moral relativism and pragmatism become inescapable. Chastity becomes defended on pragmatic grounds as socially or psychologically necessary, and becomes attacked on equally pragmatic grounds as a restraint on life.
Philosophically, man’s every attempt to establish a law or universal likewise fails. Without an absolutely sovereign God and an infallible Word, every universal is inevitably a construct of the human mind…
Thus, to hold that man alone speaks in Scripture is to destroy not only the truth of Scripture but all truth and to reduce all knowledge to subjectivism and relativism. Man indeed becomes an island in himself, hearing no voice but his own, and committed only to suicide. [Philosopher Friedrich] Nietzsche’s nihilism is the only consistent exposition of this position; every attempt on his part to establish a universal without God and Scripture failed.
- AmesG (2007). Essay:Social Effects of the Theory of Evolution. Available http://rationalwiki.org/wiki/Essay:Social_Effects_of_the_Theory_of_Evolution. Last accessed 29th May 2016
- Rushdoony, R.J. (1959). By What Standard? An Analysis of the Philosophy of Cornelius Van Til. The Presbyterian and Reformed Publishing Company, Philadelphia, p. 136