I gnash my teeth or break out in hives when I hear or see a legal scholar say or write that this or that legal field or problem is "undertheorized." This sort of statement suggests that these legal scholars believe that law encrusted with theory is inherently better than law that is not so encumbered. The statement also suggests that these legal theorists believe that coming up with good theories is just a matter of willpower and determination.
Of course, inventing theories is in fact very easy. For example, it is not hard to theorize that the world is an egg laid by a great big turtle. The difficulty, of course, is developing good theories.
There have been various verificationist theories of science, and these theories have gone wrong in various ways. But what they have in common and what remains true in them is the belief that a good theory must be put to the test -- the belief that one must, ultimately, determine whether one's theory stands up to the facts, to the actual workings of the world.
This is one big reason why evidence is or ought to be important in legal scholarship (as well as in science).
The attitude of legal scholars instead is often, "I have an alluring theory. Let me me see if I can make the pertinent legal phenomena fit my theory." This attitude is the path to perdition. It is the legal equivalent of the search for epicycles.
Coming soon: the law of evidence on Spindle Law