There are four divinely established institutions for believer and unbeliever alike: Volition, marriage, family, and national governance.
Government may legitimately enforce legislation to maintain those institutions so that encroachment upon their basis doesn't erode the rights and privledges of others, thereby defending our freedom within those institutions.
For example, we have social laws against fraud. One could also argue that any criminal might attempt to defraud his fellow man and the government has no right to interfere with the decisions of the victim, even when fraudulant intent is performed by the criminal. By enforcing the laws against fraudulant behavior, fraud might continue, but recourse may be available to those who have been victimized.
Likewise with the case of marriage. If one legalizes gay marriage, a number of unjust behaviors will no longer be controllable by legitimate authority. Where God has created a right man and a right woman for every soul life imputed by God, homosexual behavior merely victimizes the spouse of the homosexual.
In the case of family relationships, mature older generation family relationships never have the basis to form in homosexual relationships. The most prejudiced bigots in our society are homosexuals. They deny allowing the most basic understandings of the opposite sex in preference for lustful enfatuation with themselves and seeking to corrupt other people to lessen their implicit loneliness, but never persevering in fostering mature love for their fellow man.
Those who seek homosexual acceptance will also not be satiated in the legitimacy of their perversions. Most if not all homosexuals are stimulated in part by the illegitiamte nature of their lusts. As they mature in their degenerate behavior, they naturally reject anything righteous and just, and will further degenerate into attacking other institutions established by God. They will attack national governance, family, and even the free will of their fellow man.
There is nothing immoral in enforcing the illegitimate nature of sexual perversion and homosexuality. Conversely, legalizing and encouraging its promotion will result in loss of national, familial, marital and individual freedoms.
"Where God has created a right man and a right woman for every soul life imputed by God,..."
Almost as if you copy-pasted it out of Plato's Symposium. Greek mithology at its best.
Of course a christian might have a hard time defending the statement above.
"As they mature in their degenerate behavior, they naturally reject anything righteous and just, and will further degenerate into attacking other institutions established by God."
This particular statements is wrong in so many ways... Imagine what people would do if the statement above was targeted at christians instead of gays.
"They will attack national governance, family, and even the free will of their fellow man."
Do you even know what the religious meaning of free will is? Free will is a permission of god for men to live their lives as they see fit (judgement is supposed to come later).
Not allowing gay marriage is an attack on free will :D want to go against the word of god?
"Conversely, legalizing and encouraging its promotion will result in loss of national, familial, marital and individual freedoms."
Still so sure of that? I'd say it's vice versa... limiting freedoms is like a snowball going down the hill, good if you want to build a big snowman that won't melt till the spring, but bad if you're living at the base of the hill when the landslide hits.