With respect to the U.S. government, everyone deserves equal rights under the law. Civil union partners should get the same benefits as married couples. The military has fully accepted gays, so should other arms of the federal government. It's time to end the bigotry towards gays and fully accept them into our society, much in the same way we did with African Americans in the 1960s and 1970s.
Actually, what the government should authorize is a civil union for every couple whether gay or straight. Then the religious or other tradition of the person should dictate whether or not one wants to turn this into a marriage in the eyes of that tradition. The civil union should be the basis for the rest of it.
If you're going to make the claim that civil unions are equivalent of marriage, make them the equivalent of marriage. People want to see their significant other if they're in the hospital, they want the tax benefits. They want to be treated equally which is a thing that needs to be done if we're going to try to sell them on the concept that they are. Right now civil unions are little more than a "here take this and shut up" token which really isn't any kind of progress.
I do not believe civil unions should be fully legal with respect to United States government benefits. Some people chose civil union over marriage to avoid higher tax brackets, in legalizing them for benefits would also mean that many tax laws would need to be changed as well. Civil unions are too vague and are not a substitute for legal marriage.
I personally do not see any benefits from marriage out of the United States government. While there may be a few benefits, especially with social security, the average married couple simply tends to pay more taxes. I believe there are many people in civil unions that would prefer to continue being treated differently than that of married couples.