I’m not sure what you mean by a strict moralistic view of marriage.
If you are a strict constitutional constructionist as well as a libertarian, ask yourself whether those who wrote the constitution (as well as the 14th amendment) thought that it provided for same sex marriage.
I personally doubt it.
Marriage was given some particular governmental benefits because it as an institution was seen as a benefit to society. Man and woman, in marriage, provided that there would be a next generation, and raised and educated that next generation. Children benefited by having a mother and a father (as is, of course, the natural order of things.)
If a homosexual couple had said they wished to have children, the first question to be asked would be “How?” Of course, now they can design their own, through various genetic technologies and the use of sperm donors and egg donations and womb renters.
The next question would have been “Why?” What good social purpose could be served by sanctioning such an unnatural arrangement? Is it of any benefit to society? Should it receive government sanction, any more than polygamy, or polyandry, or man-child marriage?