Progressives: racism in the criminal justice system
Conservatives: high propensity of young African-American males to commit crimes
Libertarians; the war on drugs
Progressives prefer the oppressor-oppressed axis, which makes racism the desired cause. Conservatives are most comfortable with the civilization-barbarism axis, which makes criminal behavior the preferred cause. Libertarians prefer the freedom-coercion axis, which makes the war on drugs the preferred cause.
He then makes this point: "Each of these causal forces has an element of truth, or at least plausibility. The chances are slim of coming up with an empirical analysis that decisively rules in favor of one cause and rules out all other causes." I come to a similar conclusion in an earlier post: that each language has some element of truth. This is one reason why it's hard to win an argument (if that ever actually happens).