Cardinal Mahony on the Arizona immigration law

I believe that the new Arizona immigration law is a bad idea on several levels.  Cardinal Roger Mahony obviously agrees that it's a bad law, and I wonder about what others think about how he expressed his opposition to the law.  Start with this: Could a Catholic legislator vote in good conscience for the new Arizona immigration law?  If so, did Cardinal Mahony go too far in the language he used to condemn the law?  I'm interested in how we understand a bishop's responsibility to speak out on issues of concern to the Church, particularly on matters of prudential judgment.  If Catholics can disagree in good conscience about the extent to which the new law respects human dignity and the social order, and about whether it is a prudent exercise of state power, should a bishop's comments reflect that capacity for disagreement?  Or should a bishop feel empowered to speak just as forcefully and unequivocally on matters of prudential judgment as on matters of non-negotiable Church teaching?