This issue is a bit more vague, a bit harder to argue, but one that I think should be argued. My main argument against allowing homosexuals to get married is that it adds a plasticity to the definition of marriage, that once followed, cannot logically be stopped.
The argument centers on what should the definition of marriage be? Who should that include? Traditionally marriage has been defined as the union between a man and a woman. The union of two men or two women was not recognized.
However, that definition is being changed, and same sex marriages in many states