John,
I think he is just saying there is room for legitimate discussion on what the Church teaches when it's not altogether clear. This is why he qualifies that the faith is not open to "arbitrary interpretation". We have a duty to discern and obey the understanding of doctrine given by the Church. This may not always be evident, and so it can be discussed, within the boundaries of prudence and justice. One example I can think of would be the meaning of Evangelium Vitae and its treatment of Capital Punishment. A case can be made that the Holy Father established moral boundaries on Capital Punishment (cases of defense), or a case can be made that he did not establish any new boundaries, but rather was acknowledging the traditional understanding of CP but seriously exhorting civil rulers not to exercise this right except in cases of defense. When discussing this, we need to try and discern what the Church intends, not what our arbitrary opinion is. But until such time as the Church clarifies herself, there can be a legitimate time for discussion. (Of course, that time would not be at a CCD class, for example; this is part of "justice and prudence").

Remarkable timing on a new Apostolic Letter by the Pope:
"While it is true that the truths of the faith are not open to arbitrary interpretations, and that respect for the rights of others places intrinsic limits upon the expression of one’s judgments, it is no less true that there is still room among Catholics for an exchange of opinions in a dialogue which is respectful of justice and prudence."
The Rapid Development is at http://www.vatican.va/holy_father/john_paul_ii/apo...

I think Kurt's idea is a good one. I think rule 1 should also be amended so that it is consistent with rule 20: "1. People are welcome to disagree with me in the comments boxes as long as they are polite. I don't mind disagreement. I do mind rudeness."
At least if Comments were disabled then people would not get the misleading impression that people were free to present a range of views on the moral question.

Is there any chance that we could have a link to "Rule 20 of Da Rulz" at the end of any post to which you think this rule applies? That way, we'll know to think twice before contradicting.