Thomas Chalmers (1780-1847) in his 1829 sermon, On Religious Establishments, addresses a long-standing objection to establishments. They necessarily corrupt the Church, and history demonstrates it. The Church only declined after the Edict of Milan. But, Chalmers counters, the Voluntaries fallaciously mistake the cause. The source of the secularization was not the state – it was the Church itself. There is no fault in the contract of these two independent parties, each laboring in its own separate sphere, yet supporting each other mutually. The fault rests with the party who abuses the contract. And before the Reformation, it was not the Church that got the raw end of the deal:
“There is a kind of vague and general imagination, as if corruption were the invariable accompaniment of such an alliance between the civil and the ecclesiastical; and this has been greatly fostered, by the tremendously corrupt Popery, which followed in historical succession after the establishment of Christianity in the days 
of Constantine, and which certainly holds out, in vivid contrast, the difference between this religion in the period of its suffering, and this religion in the period of its security and triumph. But it were well to discriminate the precise origin of this frightful degeneracy. It arose not from without; it arose from within. It was not because of any ascendency by the state over the church whom it now paid, and thereby trenched upon its independence in things spiritual. It was because of an ascendency by the church over the state, the effect of that superstitious terror which it wielded over the imaginations of men, and which it most unworthily prostituted to the usurpation of power in things temporal. The fear that many have of an establishment, is, lest through it, the state should obtain too great power over the church, and so be able to graft its own secularity, or its own spirit of worldliness, on the pure system of the gospel,—whereas the actual mischief of Popery, (more…)
West Port Experiment 