I have been addressing the conclusion of the logic (and the argument behind it) which apparently holds that making a statement as fact based upon an inerrant source is a claim to assured inerrancy in speaking infallibly under certain conditions, if they indeed are engaging in the same act which we criticize Rome for, as you charged.
Which is not that Rome cannot speak truth - even if it be something as basic as “there is a Creator” and other Scriptural truths which we also affirm - but the epistemological basis for Rome’s presumption of assured infallibility and certain teachings which flow from it.
The issue is authority, and thus my question to you regarding your underlying argument was and is, are you saying that no one can have Scriptural certitude (and thus believe and speak the same) except by confidence in the magisterium of Rome when it speaks infallibly?
No, you are not.
You are denying an inescapable conclusion, positing a different argument, and treating that argument as if it were mine.
The is no "underlying" argument.