That argument is always amusing, since Roman Catholics have to make a PERSONAL INTERPRETATION of what Rome teaches them, or else Roman Catholics take everything on purely, blind trust that everything taught is the truth.
It goes like this, the pope or magesterium renders a teaching, that goes to the cardinals, who interpret what the pope and magesterium has taught.
Then it goes down to the archbishops, who interpret the cardinal's interpretation of what the pope or magesterium taught.
Then, it goes down to the bishops, who interpret the archbishop's interpretation of the cardinal's interpretation of what the pope or magesterium taught.
Then it goes down to the priest who interprets the bishop's interpretation of the archbishop's interpretation of the cardinal's interpretation of what the pope or magesterium taught.
Then each individual Roman Catholic must make a personal interpretation of the priest's interpretation of the bishop's interpretation of the archbishop's interpretation of the cardinal's interpretation of what the pope or magesterium taught.
Which is why popes, magesterium's, cardinals, archbishops, bishops, priests and individual Roman Catholics have contradicted themselves more times than Budweiser has brewed beers.
Speaking as an Anheuser-Busch shareholder AND a Catholic, I resemble that remark.
I hesitate to get in the middle of this, I hate the sight of blood - especially my own, but the role of personal interpretation is never black or white, I think, which makes arguments about them frustrating. At the risk of sounding nominalist (whatever THAT is) I like to say that whatever else the Incarnation may mean it clearly reminds us that God is AT LEAST as mysterious as anyone else you ever loved, and that finally, after all the conversation is done, the consummation of knowledge will lie in an intimate relationship of mutual self-giving.
The pseudo-nominalist part arises from my certainty that everything I say about God (except this, maybe) is more false than it is true, but it is still of very great importance to try to say what is true about Him the best we can.
But I think that your "devolution" of doctrine is a little inaccurate. The obedience and assent I owe the hierarchy and the magisterium is, especially in those areas where I have done some little study, active, questioning, and probing.
Look in an operation, I got a garbled radio command: Bogie is running from the North gate of the stadium toward the West gate. (I'm at the Southwest gate.)
There's not time to question. My partner runs toward the west gate on the outermost way, I take the middle way while scanning to my right at another way he could be running. At the end of the story I come upon a pile of people just in time to grab an arm sticking out so that somebody else can cuff it.
I didn't know much, I had lots of questions, but there was no time. I obeyed the best I could, success: cuffed bad guy having the pepper spray washed off his face.(A very pleasant bad guy as it happened, just gets a little rowdy in his cups -- all in good fun.)
Later I ask the captain WHY the #*#@#*%! he didn't give more a precise description of where the bogie was -- and we began developing a new approach to communications.
But however precise we get, in the event there will always be personal interpretation to some unavoidable exten. But it's important for the entire team to be speaking the same language and to have basic notions decided. We're at war here, and it shouldn't be against each other.
I'm not sure how far to take the analogy, but I think it has some usefulness.