Focus on the Family’s CitizenLink is eliciting responses from Christians concerning their feelings and experiences of family – of family defined by a marriage between one man and one woman and their children. They have posted on their website a sampling of the responses received thus far:

Be Sure to See Our Special “Why Marriage Matters” Report
A few weeks ago, we asked you to submit your thoughts about why marriage matters — to society as a whole, and to you and your family. We received more than 500 responses — some of them humorous, some of them heartbreaking, all of them heartfelt.
We’ve compiled the top 25 responses, and urge you to read them by clicking on the link below. We hope they each shed a little more light on why this God-created institution must be protected.
http://www.family.org/cforum/extras/a0032519.cfm

Of course marriage matters. For this group of people, gay-marriage demands the destruction of the institution of marriage. Their conclusion, seen in the proof of the testimonies given by people as posted above, is untenable because of the belief that anyone favoring gay-marriage does not believe that marriage in fact matters. The institution of marriage will collapse if gay people are allowed involvement in the institution, according to anti-gay prohibitionists.
I have not read all the 25 responses. From what I have read, the conclusions drawn by anti-gay-marriage people do not necessitate exclusive male-female relationships. As more and more gay couples become visible and as more and more rational, stable, and mature children are raised in these relationships, people will see that the claims made by Focus on the Family and the anti-gay-marriage forces are not true. There may very well be differences, but even if there are differences, they cannot be known at this point. Will there be dysfunctional children raised in dysfunctional gay-relationships? Yes, of course. Does that then mean gay-relationships are always wrong and destructive to children and the men/women involved? No more then the relationships of dysfunctional straight-families producing dysfunctional children means heterosexual marriages are always wrong and destructive.
The lines of argument being used by anti-gay-marriage forces are simple untenable when seen in the light of reality – reality as determined by God as revealed in Scripture and humankind.