"But in your hearts set apart Christ as Lord. Always be prepared to give an answer to everyone who asks you to give the reason for the hope that you have. But do this with gentleness and respect, keeping a clear conscience, so that those who speak maliciously against your good behavior in Christ may be ashamed of their slander." ~ 1 Peter 3:15-16
Sola Scriptura & Roman Catholicism

What I think is the critical distinction between the Roman Catholic and Christian boils down to the Ultimate Authority of the Scripture. The Roman Catholic thinks that he cannot correctly "interpret" the Scripture for himself. This does not mean that he is not engaged in the act of interpretation, for he must certainly interpret what he reads or the information he processes, but that he couldn't be certain if his "private" interpretation is correct. This is why he has to turn to the RCC as the infallible interpreter for all (infallible) interpretations of the Scripture.

The Christian disagrees with the notion that the RCC is infallible since the Scripture does not lend support to such a notion. Moreover, how does the Roman Catholic be certain that his private interpretation that "the RCC is infallible" is infallible to begin with? If the Roman Catholic's private interpretation is not infallible, will he then admit the possibility that the RCC is really not infallible after all? The Christian notes that saying the RCC is infallible because RCC says so is begging the question. If the Roman Catholic says that the Scripture says that the RCC is infallible, because the RCC says that the Scripture says so, then we ought to test the claim against the Scripture (which is Sola Scriptura).

Apparently, RCC failed the test. The Christian affirms that only God alone (and His words) is infallible, and not created beings (including the RCC). Moreover, the Scripture is not encoded in code words or as difficult to understand as the Roman Catholic claims it is. The fact that all christians (without subscribing to the notion that the RCC is infallible) can and do agree that Jesus Christ is the only Way to salvation as written in the Scripture, refutes the point that we cannot know what the Scripture says without RCC as an infallible interpreter.

Moreover, is there really a need for the written Scripture if a line of living infallible interpreter or messenger will be always around? The Scripture is sufficient to function as the sole, infallible rule of faith. While the Christian tests everything (including the RCC) against the Scripture, the Roman Catholic has to follow the RCC's interpretation when his private interpretation deviates from the RCC's interpretation since the RCC is presumed to be infallible.

The implication is that the RCC is able to introduce new doctrines not found in the Scripture, or interpret it in such a way that it appears to be in accordance with the Scripture. There is no room for the Roman Catholic to disagree with the RCC's interpretation or verify if the RCC is truly correct in its interpretation, since by definition the RCC must be infallible. When the Roman Catholic's interpretation deviates from the RCC's interpretation, the RCC's interpretation must be submitted to and acknowledged as correct irregardless of what the Scripture really says.

At the end of the day, the RCC has yet to prove that there is an infallible interpreter and that she is the one. Surely if God intends for an infallible interpreter, He would have make it plain obvious to His people so that there’s no argument over it, wouldn’t He?