This is an update of my post below on "moderate" Murphy.
I'm currently working through a (very interesting) six hundred and fifty page ethics tome by Fr Austin Fagothey (who was professor of philosophy at Santa Clara University) entitled "Right and Reason."
In here he speaks about moral positivism (not to be confused with the positivism of Auguste Comte). Moral positivism comes in three forms. One that says that morality comes from the dictate of the State, another from custom and the third from the will of God. All of them are wrong but it is the first that is of interest here.
The idea that something is right or wrong only because the state commands or forbids it comes from two men: Thomas Hobbes and a Frenchman by the name of Rousseau. According to Hobbes (in an excerpt quoted by Fagothey), before the existence of states there was no morality -nothing intrinsically good or bad.
Of course, the State has the authority to make laws concerning things that are otherwise morally indifferent (such as that you have to stop at a certain place because there is a stop sign there). Such a thing's moral goodness or badness then becomes extrinsic.
As someone was telling me recently, in his day Hobbes was in danger of being put to death on the charge of atheism (something he was able to wiggle his way out of). Yet, fifty years later many bishops had unknowingly adopted many of his ideas.
I think we can say that three hundred years later Cardinal Murphy has imbibed this particular idea of Hobbes'. Taken to it's logical conclusion it brings horrifying results.
The reason I extrapolate on this is it is not uncommon to find people unthinkingly adopt this outlook without realizing what it entails. "How can that be wrong? It's legal isn't it?"