... with Christians and Catholics in particular.
Since the time of St. Thomas Aquinas, Catholicism has reconciled science and theology. That reconciliation is based upon a few simple precepts.
First, God does not create contradictions. Second, God has created a rational world, one that we can work out for ourselves through logical thought. This leads to the third - if established science conflicts with theology, then our understanding of theology must be revised.
In the case of marriage, not only do science and theology agree, they thoroughly reinforce each other. Biology is pretty clear on how babies are made. They come from one man and one woman. Since people are paramount in the faith, that relationship must be a special one. To say that two men or two women or two men, three women and eight parakeets are equal to one man and one woman, you have to dismiss God-given biology. In essence, you have to say that God was mistaken when He decided that all human life would come from that one relationship.
As far as I'm concerned, if the populace votes to redefine marriage, then that's the way it goes. If Bob and John in San Francisco get hitched and are recognized by the government as married, that's their issue. However, if the government somehow forces me to recognize all marriages and all relationships as equal, it's violating my first amendment rights to freedom of religion. It is forcing me to deny the biological facts given to us by God. There's no squaring that circle at all.
Just something to ponder as the weeks go by and more and more Christians end up in the tumbrel, carted off to the guillotine for not being sufficiently enlightened.