Rome rarely has infallibly defined a Scripture text, and within the (often general) parameters Rome provides RCs have much liberty to use texts to support her teachings ( often engaging in much extrapolation), though her teachings do not depend upon the exegetical weight of Scriptural evidence, not are the arguments or reasoning's behind an infallible decree necessarily infallible themselves.
As for disagreeing, besides which teachings belong are infallible (thus requiring "assent of theological faith") being open to interpretation, most of what RCs believe and practice is said to come from the Ordinary magisterium (requiring "religious submission of will and intellect"), and Catholics argue whether one may withhold assent from some of its teachings. Donum Veritatis does allow for conscientiously withholding of assent to a non-irreformable magisterial teaching (presuming he knows it is), though he is he is to refrain from speaking publicly, and be teachable and willing to submit to correction.
Conscience also is given a high priority in determining what a soul can assent to, though conscience does not constitute an autonomous and exclusive authority for deciding the truth of a doctrine.
"Over the pope as the expression of the binding claim of ecclesiastical authority there still stands one's own conscience, which must be obeyed before all else, if necessary even against the requirement of ecclesiastical authority. Conscience confronts [the individual] with a supreme and ultimate tribunal, and one which in the last resort is beyond the claim of external social groups, even of the official church" (Pope Benedict XVI [then Archbishop Joseph Ratzinger], Commentary on the Documents of Vatican II, ed. Vorgrimler, 1968, on Gaudium et spes, part 1,chapter 1.).
Understanding, and explaining inconsistencies becomes more difficult when examining all of what popes and Rome have taught, including canon law, which once forbade laymen from engaging in the kind of debate seen here.
"...Hence it is that the study of Canon Law is beset with almost inextricable difficulties, the door is open to disputes and litigations, consciences are troubled with a thousand anxieties, and people are driven to despise the law." (General Legislation in the New Code of Canon Law, pp. 70,71)
Once, when the Magisterium canonized the entire Bible declaring it inerrant and divinely inspired, wasn't enough?