Our country is made up of a plethora of religious and non-religious individuals. The only way to go is separation of church and state, regardless of what the founding fathers intended.
Right. We are not a theocracy and were definitely not intended to be. We don't want Islam's Sharia being the law of the land either, or any other specific religion's moral code. So government allows religions to practice freely. They can regulate themselves internally, but no government officials are stipulating membership requirements, beliefs, doctrines, dues, etc. We have government laws to protect citizens from generally accepted immoral behavior: don't kill, don't steal, don't lie, be honest in your dealings with each other, obey traffic signals and the speed limit, etc. These all promote a stable healthy society.
So, what about traditional marriage (between a man and a woman)? Does it help or hurt society in general? I think it is well established that it helps. Government encourages it through legislation, individuals are defined by it (single, married, separated, divorced), kids generally grow up planning on it (I know that is changing). Cities are built around families. There are activities for mom's, dad's, parents, children, and grandparents.
And, finally, to the point, what about gay marriage? Does it help or hurt society? In another post I mention one way I think it hurts society (the dilution of important labels). It also, generally, does not encourage the birth of children (even traditional marriage is struggling with that one these days). And what about the diseases that come from it (I haven't studied it so I don't know)? Isn't AIDS more common among them? What about STDs? Generally, I conclude that gay marriage is not good for society and yes, it should be legislated against and not encouraged. What am I not considering that would make it more beneficial for society?