Well certainly it's not fair that only heterosexuals have an opportunity to sell their hand in marriage to a foreigner... And what a great open-ended opportunity it is--every year over 450,000 US citizens marry foreign-born individuals, this where spouses are considered "immediate relatives," and therefore excluded from numerical quotas. Furthermore, this new citizen is in a position where he/she can sponsor relatives to become permanent residents...
Let's say a couple of same sex friends live together, isn't it wrong to say that if they get horny enough (or drunk enough...?) to have sex together than suddenly they're entitled to all kinds of extra benefits?
Personally I think there should be no marriage benefits unless there's a child involved. What's the sense otherwise? And it's not fair to the employer, ect., that for no other reason other than that a guy or gal gets "lucky" suddenly there's extra health insurance, ect. to be paid... However if there is a child, with all kinds of extra expenses involved, than it does make sense... Such is a sophisticated society...
On the other hand, I think hospital visiting rights, ect. should be extended as part of a civil union...

Civil Unions do not have all the benefits of marriage. As the previous commenter noted, civil unions are useless for immigration purposes. They care no federal benefits at all, including tax benefits. They are also meaningless in other countries. If I had a civil union with my same sex partner and I had a visa for the Netherlands, I could not get a normal spousal visa just on the basis of that civil union. They don't know what one is. They don't recognize it. Even though they have normal gay marriage.

Civil unions are no more separate but equal than the last institution so described.