Unfortunately, who's to say that it's our responsibility where to draw the line? Honestly, let's use a contemporary example. People who want public prayer in schools. I'm a good, born-again Christian, so I should be all for that, right? NOT! What if we started praying to Buddha, or Shiva, or some other deity (maybe Zeus, Huetzicoatl, Thor?) Where do we draw the line with that issue?
There's no real reason to use faith as a basis for laws, because one man's faith could not carry over into another's life. What if there was a religion that supported gay marriage, and making it illegal was a sin in that religion. What then?