On the latter point, a small bit of evidence from David Hume's History of England, the reign of Edward I (around 1297)
For this purpose, he [Pope Boniface VIII] issued very early in his pontificate a general bull, prohibiting all princes from levying without his consent any taxes upon the clergy, and all clergymen from submitting to such impositions; and he threatened both of them with the penalties of excommunication in case of disobedience. This important edict is said to have been procured by the solicitation of Robert de Winchelsey archbishop of Canterbury, who intended to employ it as a rampart against the violent extortions, which the church had felt from Edward, and the still greater, which that prince’s multiplied necessities gave them reason to apprehend. When a demand, therefore, was made on the clergy of a fifth of their moveables, a tax which was probably much more grievous than a fifth of their revenue, as their lands were mostly stocked with their cattle, and cultivated by their villains; the clergy took shelter under the bull of pope Boniface, and pleaded conscience in refusing compliance. The king came not immediately to extremities on this repulse; but after locking up all their granaries and barns, and prohibiting all rent to be paid them, he appointed a new synod, to confer with him upon his demand. The primate, not dismayed by these proofs of Edward’s resolution, here plainly told him, that the clergy owed obedience to two sovereigns, their spiritual and their temporal; but their duty bound them to a much stricter attachment to the former than to the latter: They could not comply with his commands, (for such, in some measure, the requests of the crown were then deemed) in contradiction to the express prohibition of the sovereign pontiff.The Church of the late 1200s was perhaps best placed of any party to provide private law enforcement services to its members. But it was unable to protect the Clergy when Edward removed the State's protection.
...Instead of applying to the pope for a relaxation of his bull, he [Edward] resolved immediately to employ the power in his hands; and he told the ecclesiastics, that, since they refused to support the civil government, they were unworthy to receive any benefit from it; and he would accordingly put them out of the protection of the laws. This vigorous measure was immediately carried into execution. Orders were issued to the judges to receive no cause brought before them by the clergy; to hear and decide all causes in which they were defendants: To do every man justice against them; to do them justice against no body. The ecclesiastics soon found themselves in the most miserable situation imaginable. They could not remain in their own houses or convents for want of subsistence: If they went abroad, in quest of maintenance, they were dismounted, robbed of their horses and cloaths, abused by every ruffian, and no redress could be obtained by them for the most violent injury. The primate himself was attacked on the highway, was stripped of his equipage and furniture, and was at last reduced to board himself with a single servant in the house of a country clergyman. The king, mean while, remained an indifferent spectator of all these violences; and without employing his officers in committing any immediate injury on the priests, which might have appeared invidious and oppressive, he took ample vengeance on them for their obstinate refusal of his demands. Though the archbishop issued a general sentence of excommunication against all who attacked the persons or property of ecclesiastics, it was not regarded: While Edward enjoyed the satisfaction of seeing the people become the voluntary instruments of his justice against them, and enure themselves to throw off that respect for the sacred order, by which they had so long been overawed and governed.
The spirits of the clergy were at last broken by this harsh treatment. Besides that the whole province of York, which lay nearest the danger that still hung over them from the Scots, voluntarily, from the first, voted a fifth of their moveables; the bishops of Salisbury, Ely, and some others, made a composition for the secular clergy within their dioceses; and they agreed, not to pay the fifth, which would have been an act of disobedience to Boniface’s bull, but to deposit a sum equivalent to some church appointed them; whence it was taken by the king’s officers. Many particular convents and clergymen made payment of a like sum, and received the king’s protection. Those who had not ready money, entered into recognizances for the payment. And there was scarcely found one ecclesiastic in the kingdom, who seemed willing to suffer, for the sake of religious privileges, this new species of martyrdom, the most tedious and languishing of any, the most mortifying to spiritual pride, and not rewarded by that crown of glory, which the church holds up, with such ostentation, to her devoted adherents.(emphasis added)
Sure, technology has changed over the interval, and this is hardly decisive evidence about whether Caplan or Cowen is right today. But it is worrying.
Hume's History of England provides excellent bedtime reading. General rule for arts students: read more economics. General rule for economics students: read more history.