What Mike writes is, of course, absolutely true, and I hope you remember it the next time you're taking a test in a for-credit course on Catholicism.
But when you're not taking a test in a for-credit course on Catholicism, I hope you say, "Frankly, I care a lot more about whether I'm wrong than about whether I'm a bad Catholic." Being a bad Catholic is a question of rules. "But is is true?" is a question of virtue.
Tom definitely has a point. In youth I taught myself Catholicism "to the test," and at the time I gave that more importance than it merits. I always did great in catechism and loved it, but the nuns never considered me virtuous enough even to make it to the applicant list for service as an altar boy. Later, as part of my college quest to enter a seminary, I took an extensive and tricky "Catholic orthodoxy test" given by a couple of friends studying there and almost identical to one they themselves had been given. I scored 100%. I should not have been as surprised as I was that the higher-ups found that almost irrelevant to determining my suitability for admission. Apparently, however, they found it quite relevant to determining my suitability to teach there—which they hired me to do as an adjunct, five years after having denied me admission as a student.
Even so, I believe Tom is largely missing the main point at hand. It is of course perfectly true that the question "Is one a bad Catholic for disagreeing with the bishops about topic P?" is quite distinct from, and subordinate to, the question "Is what the bishops say about P true?" But the two are nonetheless related; and if one reflexively treats the latter question as merely a matter of opinion, then one will sometimes find oneself failing to give the former question the importance it truly merits. That's because the latter is sometimes to be answered precisely by answering the former. In cases when what the bishops say about P calls for "the assent of faith" from Catholics, then the question whether what they say is true is already answered for Catholics. In cases where what the bishops say about P calls for "religious submission of intellect and will" from Catholics, then Catholics must treat what the bishops say as though it is true even if it might later turn out to be false. Only in cases where what the bishops say about P calls for neither kind of adherence is the latter question worth considering without the former.
The most important quaestio disputanda here, then, is precisely how one is to tell when what the bishops say does or does not call for either the assent of faith or religous submission. One might say that such a question betrays a quasi-pharisaical concern for getting the "rules" down pat. In some cases, it may well do that. But it is precisely the question underlying the debate between Paul of 153: Catholic Deep Fishing and myself. And its importance is quite objective, irrespective of the motives of some who raise it.