From the Free Online Dictionary:
1. Specious or excessively subtle reasoning intended to rationalize or mislead.
2. The determination of right and wrong in questions of conduct or conscience by analyzing cases that illustrate general ethical rules.
It's odd that a word would have two such antithetical usages, but one can see how the perjorative usage could have grown out of the second.
The subject arises because
Prof. Deneen takes a look at Georgetown Law's decision to permit internships at institutions which are not consistent with Catholic teachings.
The Prof sees in that decision a failure to apply the necessary casuistry to the issue.