Catholic doctrine begins Divine revelation in scripture and is aided by the application of reason and logic to creation. 

The premise behind Natural Law is that the universe is a rational system with a purpose. The purpose of each thing is given to it by God. God’s entire creation is imbued with Divine purpose. By examining the world carefully - by uncovering the essential nature of things and the laws determining what each is for, we can discern God’s plan and intentions. To thwart the natural functions that God has given is to act against God’s will. 

You want to base morality on the shifting sands of experience and the uncertainty of inductive probability? A reasoning that is inherently uncertain and only deals in degrees to which the conclusion is credible according to some theory of evidence. 

God's commandments were carved in stone - not sketched in sand.