The work from which Hart quotes is "The Mortgage of the Past," by Francis Oakley. That same work documents a number of issues that the folks at Called to Communion (a Roman communion blog) are unlikely to feature. For example, endnote 50 at page 269 highlights the fact that previous generations (i.e. before Vatican I) have been more open to the idea that the pope may fall into heresy:
Decretum, D. 40. c. 6; ed. Friedberg, 1879-81. 1:146. Tierney, 1964, 119, notes that even the high papalist decretist Alanus Anglicus [fl. A.D. 1190-1215] conceded that deposition would be called for in the case of papal heresy. The more moderate decretist Huguccio [of Pisa] went further, and envisaged any notorious papal crime as cause sufficient for the imposition of that penalty. For a full synoptic treatment of the origin and destiny of such notions, see Oakley, 2003b.Oakley endorses the idea that "no other pope was as important for edging papal monarch toward absolutism" as Innoncent III (A.D. 1198-1216), quoting Kenneth Pennington, The Pope and the Bishops: the Papal Monarchy in the Twelfth and Thirteenth Centuries (Philadelphia: University of Pennsylvania Press, 1984), p. 58.