That sounds like a statistical approach. More marriages not resulting in divorce is not necessarily a preservation of strong families.
You wrote: "If folks trying to get married were not men and women, no marriage." I proposed leaving that responsibility to the churches. Can we trust the government to uphold that standard, more than we can trust the churches? I think not.
Statistics have shown that children in "weak" marriages, that is parents who feel personally unfulfilled, still ending up having less social pathologies than those who grow up without a mother and father. A mother and father act as a support system and guard dogs from the outside world. There's a reason that predator's target children in broken homes. secondly, we can trust the government to uphold that standard because no people has ever voted for homosexual marriage. Even now, it is being imposed by courts. In a democratic republic, the people can, and must be, trusted to guard their social institutions. The trouble we have had has not come from the exercise of democratic will. It seems to me that libertarian minded people have some paranoid fear that their fellow citizens cannot be trusted with guarding society's traditions.