"Catholic traditionalists will, of course, say, 'Who cares,' because morality is not determined by popular vote but by the law of God. A powerful argument, but what is the data telling us?"
The second sentence is superfluous and only an excuse to continue a futile argument.  People will believe what they will, regardless of the tenets of a particular faith.  If, unlike the LDS, there is a belief in a baseline of truth in a hierarchical Church, with Christ as its Head and guided by the Holy Spirit, current opinion is not an argument for any change.