Prager - You make the cardinal mistake all same-sex "marriage" proponents make: attempting to redefine the word "marriage". Marriage was ordained and defined by God as being a union of husband and wife for the purpose of raising a family. Neither you nor any other person or government on earth have the authority to change that definition.
Second, the reason no moralist from your list has ever posited the morality of same-sex unions is because it is a self-defeating principle. Marriages create families which go on to create more marriages and more families. Same-sex unions can not follow this pattern and effectively remove themselves not only from the gene pool, but from the lineage of mankind.