I don’t think religion should be used as a rationale for either side of the debate. This is an individual rights question. Religion should have no bearing on the law in a pluralistic, secular and constitutionally-governed freedom-loving nation.
Free individuals have an inalienable natural right to engage in voluntary, peaceable private behavior that does not violate the rights of others.
No gay marriage (or union, agreement, contract) violates in any way or brings injury to the rights of any others.
This then brings up the question of government involvement in the institution of marriage. Some claim that marital protections and privileges are unevenly distributed between heterosexual couples and homosexual couples who wish to marry. That is, that the law is discriminatory based on sexual orientation.
This is true. The law is discriminatory because the government is forever in the business of choosing favorites and picking winners and losers in both social life and the marketplace. This is not the proper function of government. Its proper function is in the protection and preservation of individual rights.
The solution to discriminatory marital law is to completely remove the government’s interest in promoting or denying marriages of any kind and confine its involvement in marital agreements to the enforcement and adjudication of contract law.
This solution maximizes liberty while respecting the individual rights of free people.