Society will suffer because the families that form its basis lose their stability; an affect that will have repercussion for future generations. If homosexual "marriage" is universally accepted as the present step in sexual "freedom," what logical arguments can be used to stop the next steps of incest, pedophilia, bestiality, and other forms of unnatural behavior?
If that does happen then it is a problem between those two and not the outcome of two guys or two girls getting married. Although it is true that kids without a mother or father are deprived of the unique advice mothers and fathers give depending on if the relationship is lesbian or gay it doesn't matter.
The US Constitution contains no explicit right to marry.