President Obama's declaration in favor of gay marriage is right in principle. Americans who promise to live together as a monogamous couple should enjoy the same legal benefits, whether they are heterosexual or homosexual. The Constitution's provision of equal protection under the law enshrines this idea, and it should be extended to gay and lesbian people. However, we would achieve that result through civil unions for all couples, gay or straight, rather than through marriage.
Marriage traditionally has been a rite of the church, and it should remain so. The government should not have a hand in it. Rather, the state should sanction a contract between two people as a civil union. If, in addition to a civil union, a couple wishes to be married by a religious institution, that should be a matter between them and their community of faith.
Other nations have adopted this model and it functions quite well.
The drawback of this proposal is that many of the legal rights that flow from marriage are couched that way in the law. But that is a bump in the road that can be fixed. It's not an insurmountable obstacle.
The advantage is that many Americans object to same-sex marriage because they view marriage itself as a religious sacrament, and many churches deny it to homosexual couples because they hold that homosexuality is a sin. People of faith who take this view worry that if the government extends marriage to include homosexual couples, that definition could be forced on their churches.
If there were a separation of church and state where marriage is concerned, however, that fear would no longer be an issue. Everyone would be treated the same under the law. Gay couples and straight couples could obtain civil unions, and they also could obtain marriages, depending, of course, upon the doctrines of various churches. But one contract would be a civil institution and the other would be religious.
The rights of American couples would be the same regarding privileged testimony, the raising of children, inheritance, hospital visitation, insurance benefits, all the things that currently matter to all couples, whether they are a man and a woman, a man and man or a woman and a woman. Basic fairness and equal treatment under the law demand no less. This could be achieved through constitutional amendments in the states.
Unfortunately, the trend in recent years has been in the opposite direction. Many states, including Utah, have passed amendments limiting marriage to heterosexual unions. Civil unions would be fairer a more civil answer, if you will.