In the absence of clear evidence against them, I make assumptions in favor of personal freedom, markets, federalism, and limited government. Since these are not synonymous, there will be tension. I suppose that morality, such as the marriage tradition, is a product of biological and social evolution and the supposition that a custom we don't understand has no purpose and can be dismissed is as risky as the supposition that an organ we don't understand has no purpose and can be surgically removed without cost would have been in the days before scientific physiology.
The entire gay marriage argument originated in State intrusion into labor markets. If governments paid their employees in cash (no employer-funded medical plans, no workmen's comp, no retiree benefits) and left private-sector compensation to employers and employees (no State-mandated benefits), the legal definition of "marriage" would not matter. Any number of people could set up house and promise to love, cherish, and obey each other without imposing costs on others. Currently, spousal benefits put taxpayers on the hook for costs of dependants of government employees. That's my principal objection to the court-mandated redefinition of "marriage". Redefinition of marriage to include same-sex couples is a tax increase.