Sensible moral reasoning begins with concrete, specific cases. For example: It would be wrong for me to walk over to Robin right now and punch him. From there, we can start to generalize. It would probably be wrong for me to walk over and punch any of the people in this room. At the same time, we can note exceptions. If Robin had consented to box me, then punching him would be OK. In fact, it would probably be wrong not to try to punch him, because I'd be cheating you, the audience.
That's argument by cases of consciences, and such argument is casuistry. I agree we need a genuine casuistry; it's lack has left a void that has been filled by ridiculous trolley problems. (Trolleyology, I once joked to someone, is the devil's version of casuistry.) But it's clear enough, as well, that casuistry on its own doesn't get you far at all. Pascal in his Provincial Letters bent or broke more than one truth, but his attack on casuistry was surely right in one respect, namely, that casuistry alone leads to moral absurdities; and big moral absurdities are moral abominations.
Tyler Cowen also has an interesting comment on Caplan's piece:
My overall view is that ethical intuitionism settles many fewer issues than most of its proponents like to think. That said, there is often nowhere else to go. We somehow need to come to terms with two propositions at the same time:
1. We need to think more rather than less ethically.
2. The content of ethical philosophy tells us less, in reliable terms, than most people would like to believe.
Which are both right. But contrary to Cowen's suggestion, I think it's clear enough that this is because we have no developed casuistry -- it's casuistry that gets into the real details of the ethical life and the ethical society. But what we have is a very degenerate form of it, consisting of very few tools for analyzing cases and of almost no forms of inference beyond analogical reasoning. That's not going to get you much. One might as well try to build a ship and go to the moon with nothing but free-body diagrams of inclined planes.