For good reason!
On a religious basis it is not acceptable behavior. It is in direct opposition to how we are supposed to try and live our lives.
From a secular view promoting a deviant unhealthy behavior as "good and normal" is self destructive. From a govt view, marriage is important because it creates the best structure for children to become part of the nation and to be sound citizens. Marriage creates a contractual arrangement that protects the family structure.
Homosexual marriage from a secular view does nothing for the benefit of a nation. Children are not born in a homosexual marriage. Children are not raised in an environment that leads to more children being born, instead they are adopted into the single sex environment and are taught this is normal.
If a govt does not actively pursue policies that keep the nation healthy and growing in time the nation will decline and be dominated by younger more aggressive nations. In this sense defending marriage as the union between a man and a woman is a defense issue.
The problem we have is a majority of the country has now bought into the idea that everything is okay "as long as you don't hurt anyone" and why should we treat homosexuality different than civil rights. As a religious people the answer is obvious. GOD tells us it is wrong and unnatural. However, the popularity of homosexual rights and marriage increasingly show we are not a religious people anymore.
It is also a FACT that there are federal aspects to marriage whether people like it or not because people move from state to state.
Another FACT is the homosexuals have the exact same marriage rights as everyone else and they always have. There is NO LAW that prohibits homosexuals from being married. Moreover, it has ALWAYS been an option for homosexuals to enter into legal partnerships with each other.
Libertarians are the ultimate statists, they worship the utterly false idea of "states rights" and are all to happy to place these "states rights" over our rights. Under the libertarian mantra a state should have the "right" to allow incestuous marriage on any level, polygamy, infanticide and any other form of depravity it wants. The conservative movement needs to sever its relationship with libertarians and it needs to happen immediately.
Homosexual cultures must fail because they are self-indulgent and overlook stability. That is the case with our current American culture. The homosexuality is a blatant sign of self-indulgence, and the inability to reign in spending is one manifestation of that self-indulgence.
It is the drug addict spending every last dime on his self-indulgent addiction, and then begging, borrowing, and stealing when his resources are dried up to continue his self-indulgence.
Such a society is destined to fail.