Here [1] is an interesting article about the claim made by campaigners for same-sex “marriage” that their campaign is 
analagous to the civil rights struggle in the US. The author, Thomas M Messner, says that the analogy breaks down for a couple of reasons.
“Marriage is not fundamental to our “existence” and “survival” merely because it sometimes is marked by expressions of love, commitment, and respect. Marriage is fundamental to our existence and survival because it remains society’s best and most effective way of ordering sexual relations between men and women, encouraging procreation, and increasing the odds that a child will have the influence and support of both a mother and a father.”
Messner contests the argument that civil rights legislation wasn’t popular. He says that the popular will of the American people had turned against laws maintaining racial prejudice.
“The same can’t be said about marriage. If imposed through federal courts, same-sex marriage would fly in the face not only of popular will but also longstanding traditions and nearly universal understandings of marriage.”
It might also be pointed out that yet another way in which the analogy falls down is the fact that, in terms of interracial or interreligious marriage, while those who contracted them might have been socially ostracised, this was mainly for customary reasons. No-one claimed that the marriage as a marriage was invalid, or redefined the concept of marriage. This is not the case for same-sex “marriages”.