Lots of problems. For one is the impermanence of such unions. Homosexuals are extremely promiscuos. For another we have the problem of children being adopted by such degenerates. Another problem is the tremendously large percentage of pedophiles amongst homosexuals. You will notice that no homosexual organization has ever attacked LAMBDA the organization which promotes love between adults and young children.
But most important though is that the family is the center of any society and by diluting the benefits of such unions we are encouraging the breakdown of the heart of a good society.