States place many restrictions on adoptions. China, for example, does not permit adoptions by couples who are too old, have disabilities or are obese1. It doesn't mean that there is anything wrong with being overweight, old, or disabled. But the Chinese authorities are trying to decrease the likelihood of the adopted child losing a parent before the age of 18, which for these kids can be especially traumatic. If the parents being gay can be shown to be inherently harmful or less desirable for a child than straight parents, then such a ban would not constitute discrimination. It would be a decision based on a relevant and valid criterion.  1 Belkin, Lisa. "An End to Gay-Adoption Bans?". New York Times. 28 July 2010 .(accessed 2 August 2011)