"Both my son (15) and I have just been amazed at why sooo many evangelicals, catholics, and mormons seem to care about nothing else other then what gay couples are doing . . . boggles the mind . . . "

I've heard evangelicals relate their thought process to the idea of collective punishment from God.  That is, that they believe the nation as a group is harmed by supporting what they see as something against God's laws.  It think that's not only BS but also bad theology, but you asked why . . .