You can mention something like if someone is raised by a same-sex couple, they might not have an experience of being raised by parents of opposite sex. So if say a girl was adopted by a male-male couple, then there would not be the "women to women" understanding that might be achieved with a women-male couple. So things like talking about monthly cycles, proper female etiquette, etc. would have to be taught by the use of the books rather from personal experience. So with hypothetically speaking, a child that raised by a same-sex couple might be raised in an environment that is viewed from one-gender perspective. So say the son that is being adopted is not gay, and eventually wants to start dating, well if he is to ask advice from his parents, then he would receive the perspective of one gender, specifically that of a homosexual viewpoint.
Basically, with a male-female parents, you might have this "more balanced" views, since they would be the combination of a parent of one sex and the parent of another sex. And with homosexual parents you might have views that are sided to a specific gender.