William Junker on Stem Cells and Natural Law

I received the following communication from William Junker:

Apropos your questioning whether natural law can have any 
role to play in deciding the fate of stem cells, I thought 
it might bear mentioning that Aquinas himself is rather 
modest about what natural law can get you: only the primary 
precepts, such as seek good avoid evil, procreate, etc. seem, 
on Aquinas' own view, indelibly imprinted on our hearts.  The 
secondary precepts of the law, in my understanding at least, 
follow from these first precepts but not in a way that they 
are immediately evident to all.  I believe Aquinas cites the
example of the German tribes who, purportedly, thought
stealing was o.k. to make just this point.  I'm sure you know
all this, but I thought that your concerns regarding natural
law's efficacy in this arena could be made more pointed if 
you made the argument that it is irrational to suppose that 
in our current society one could persuasively argue just 
from the primary precepts of the law to such a nice 
conclusion as that one concerning stem-cells.  If anything, 
the First Things folk are guilty of trying to extend the 
reasons of natural law beyond the point to which it is 
reasonable to expect them to reach.