Marriage is the union of one man and one woman, consummated by the marriage act in the hopes of begetting children and rearing and educating them.
To speak of two people of the same sex getting married is an oxymoron; it cannot happen, by the definition of marriage. There is no hope of fruitfulness in a same-sex union. The institution of marriage presumes permanence, exclusiveness and fruitfulness. So there is no way two people of the same sex can achieve what is defined as marriage. Trying to force this is like trying to force the earth to reverse its direction of spin on its axis. Try as you may, it will not happen.
Another very compelling reason not to destroy the definition of marriage is that "same-sex marriage" would be discrimination against children. Studies around the world, including by the American Psychiatric Association, have shown that children thrive and do best in life with both a mother and a father in the home. There is an intrinsic need for children to be connected to their biological mother and father. The duty of the state is to protect its citizens, and there is no one more in need of protection than children. We cannot allow children to be brought up in a home where two people of the same sex are posing as their legitimate "parents." This would be a lie and would do great damage to the developing child. (Traditional adoption is completely different, as there is a man and woman, who are legally married and still live in the hope of fruitfulness.)
Children need truth throughout their formation and to mislead them as to the proper structure of family is unthinkable. This social experimentation will have disastrous effects on our children in upcoming generations, and society will not endure this devastating deconstruction.