The consolation prize of human rights.
While some people think gays should settle for civil unions, others think they should have the right to marrige.
A type of quasi-marriage some places (in the US) offer for gays and lesbians. Its marriage, but not quite marriage. It is like 'seperate but equal' in that it is inherently discriminatory.
One drinking fountain was for whites, the other was for blacks, but the one for blacks rarely worked right.
In most places in the United States only straight people can marry. For gay people, civil unions are the 'seperate but equal' answer.