Rev. Harry R. Jackson, Jr. writes in Town Hall about why marriage must mean something rather than whatever we want it to mean:
... I would be among the first to admit that marriage as an institution was terribly weakened by both the no-fault divorce laws first passed in the 1970s and by a general willingness of our culture to separate marriage from childbearing. Neither of these factors had anything to do with homosexuality, and both dealt severe blows to the strength of American families. However, these are not reasons to further weaken marriage by defining it out of existence. (I am not the first to observe that words that mean everything mean nothing, and “marriage” is headed down that very road.) The enfeebled state of marriage today is all the more reason to fight to preserve it and hopefully to restore it to its former strength.
At the heart of the marriage argument is whether marriage exists primarily to satisfy the needs and wants of adults, or to provide the optimal environment for nurturing the next generation. If marriage is only for individual gratification, then there is no reason to restrict it to opposite sex couples. Marriage has always been the union of one man and one woman because children need one mother and one father.