Women Priests and Sin

I may be opening up a hornet's nest here, but perhaps the summer doldrums need a bit of a shake-up.  A reader emailed me John Paul II's apostolic letter on the ordination of women, in which he concludes that "in order that all doubt may be removed regarding a matter of great importance, a matter which pertains to the Church's divine constitution itself, in virtue of my ministry of confirming the brethren (cf. Lk 22:32) I declare that the Church has no authority whatsoever to confer priestly ordination on women and that this judgment is to be definitively held by all the Church's faithful."

John Paul II's statement appears, at least to my non-expert reading, to suggest that I am in a state of sin if I do not subjectively agree with the position that the Church has no authority to ordain women.  This seems to go beyond a call for deference to Church authority, equating a contrary internal conviction on women priests with sin.  (In which case, according to the Salon article, 60% of American Catholics are in a state of sin on this issue.)  I'm new to this debate, and I still tend to carry a Protestant sensibility on matters of individual conscience, but is this what John Paul II is asserting, or am I misreading him?  If I believe that women should be ordained -- or even the less confrontational claim that we should work toward the day when it is possible for women to be ordained -- does that belief itself constitute a sin?

Rob