It's not the government's job to sanction heterosexuality or homosexuality, nor is it in a position to judge the marriages of its citizens. It is not the government's job to make policy based on religious precepts, but to enforce the Constitution. The Constitution says everyone gets equal treatment under the law.
Consider if you did not have these rights to protect your family. Because gays cannot marry, they have no right to: accidental death benefit for the surviving spouse of a government employee; appointment as guardian of a minor; award of child custody in divorce proceedings; beneficial owner status of corporate securities; Bill of Rights benefits for victims and witnesses; burial of service member's dependents; consent to post-mortem examination; continuation of rights under existing homestead leases; control, division, acquisition and disposition of community property; criminal injuries compensation; death benefit for surviving spouse for government employee; disclosure of vital statistics records; division of property after dissolution of marriage; exemption from claims of Department of Human Services for social services payments, financial assistance or burial payments; exemption from conveyance tax; funeral leave for government employees; income tax deductions, credits, rates exemption and estimates; inheritance of land patents; insurance licenses, coverage, eligibility and benefits organization of mutual benefits society; legal status with partner's children; making partner medical decisions; nonresident tuition deferential waiver; notice of payment of wages to a relative of deceased employee; payment of worker's compensation benefits after death; permission to make arrangements for burial or cremation; proof of business partnership; qualification at a facility for the elderly; real property exemption from attachment or execution; right of survivorship to custodial trust; right to be notified of parole or escape of inmate; right to change names; right to enter into premarital agreement; right to inherit property; right to purchase leases and cash freehold agreements concerning the management and disposition of public land; right to sue for death by wrongful act; rights and proceedings for involuntary hospitalization and treatment; sole interest in property; spousal privilege and confidential marriage communications; spousal immigration benefits; status of children; support payments in divorce action; vacation allowance on termination of public employment by death; veterans' preference to spouse in public employment; in vitro fertilization coverage; waiver of fees for certified copies and searches of vital statistics; and probate proceedings, to name a few.