On some people's list, religion is the number one reason to keep marriage between one man and one woman. On my list, religion is number 26.LOL I have yet to hear one valid reason, religion certainly isnít one.
Kant offered a way to decide if an act or policy is moral without using religion; ask 'What if everyone did it?' If making a policy or an act a universal law produces bad results then the policy or act is bad. If same sex marriage was universal it would mean an end to mankind or an end to monogamous marriage.
Reason 13 for keeping marriage male/female; Kant's Categorical Imperative.