The thing is, married couples have rights that non-married couples don't have. They can adopt children, for example, or have legal protection to rent homes. And the government schools tend to promote "normal" marriage in textbooks, etc.
If gays can get the legal status of "married," then they can sue to have their "normalized" status promoted in school textbooks, they can sue landlords who don't want to rent to fudgepackers, they can adopt children, they can sue organizations that provide help to those wanting to escape the gay lifestyle, they can demand Christian charities accept their lifestyle, and so on.
It has real consequences.
Securing the nation's borders is, however, probably the main task of any government. It'd be nice if this government got around to performing this task.
But, but, but you just don't understand. What good will it do by securing our borders when the gay mariage will end society as we know it right from within our borders. The very existence of marriage between man and woman is being threatened before our eyes. A constitutional ammendment is our only chance for survival. The future of civilization is at stake here.