Because I don't believe homosexual coupling is good (for reasons listed elsewhere in this thread), so I don't believe that the government should promote it. As I stated originally, it's not a forgone conclusion that the reasons we want to promote heterosexual coupling are not necessarily applicable to homosexual coupling.
I do believe that heterosexual coupling is good, and I believe that it's good for the government to accept that marriage is a near-universal practice and its implementation may be codified officially in law and modified by nuptial contracts where applicable rather than leaving the whole thing blank, waiting until a legally illiterate spouse because widowed and/or abandoned, and leaving that person with no recourse against the abandonment and/or death, mechanism to gain control of shared property, etc. I think it's debatable whether the government should be in the business of providing less crucial incentives, like tax breaks, or whether that operates best as a non-governmental function.
I do believe that heterosexual coupling is good, and I believe that it's good for the government to accept that marriage is a near-universal practice and its implementation may be codified officially in law and modified by nuptial contracts where applicable rather than leaving the whole thing blank, waiting until a legally illiterate spouse because widowed and/or abandoned, and leaving that person with no recourse against the abandonment and/or death, mechanism to gain control of shared property, etc. I think it's debatable whether the government should be in the business of providing less crucial incentives, like tax breaks, or whether that operates best as a non-governmental function.