Glenn Stanton is the director for Family Formation at Focus on the Family and author of Secure Daughters, Confident Sons. He explains at NRO why it is false to compare Loving V. Virginia to laws defining marriage as between one man and one woman:

Folks like Joan Walsh at Salon and Jonathan Capehart at the Washington Post have taken the 44th anniversary (June 12) of Loving v. Virginia, the Supreme Court case which struck down state prohibitions against blacks marrying whites, to puff a new video by the “dynamic duo” of Ted Olson and David Boies (co-councils in California’s Prop 8 case) lecturing us all on how that truly nasty injustice then is the precise injustice gay and lesbian couples face today. This is a very persuasive argument, not because of its logic, but solely for the emotionalism it stirs. The two have nearly nothing in common.

Segregation was a profound social evil. Full stop. Marriage as an exclusive heterosexual union is a necessary social good. It is why all cultures since earliest days, regardless of religion, law, or culture, have marriage as only between men and women.