There have been LGBT parents, and even same-sex parents, raising kids since the dawn of time. As a gay parent you should know that.
Just because our relationships are finally becoming legally recognized it does not mean that same-sex relationships, or LGBT parents, are new. Perhaps there haven't been as many studies examining our lives as there could be but that doesn't mean our family structures are some sort of "new social experiment" with unknown outcomes.
Yes, I am VERY well aware of that fact -- my own grandchildren are proof of it -- and I would never suggest that mine was some kind of "social experiment." HOWEVER ... until we start tracking same-sex marriages and formally gathering data, we won't have significant statistics available to prove our case, just as it has been impossible to prove scientifically that homosexuals are born that way until someone started spending serious money on actual scientific experiments that could be published in respected journals.
The Netherlands' same-sex marriage legislation in 2000 was a VERY significant event -- the first country ever, soon followed by a host of others -- and once the children born under those official marriages start reaching adulthood in another 5 years or so we will then begin to have a significant body of data to refer to, rather than the empirical evidence, or lack thereof, for all those centuries past that you refer to. Calm yourself down -- I'm a strong proponent of same-sex marriage just like you.
To get back to the point of this discussion, all I'm saying is that is does our cause no good to misquote our opponents or twist their words into something they did NOT say. George Will did NOT say that there will NEVER be any evidence about gay marriage, as the article implies, but that there is not YET sufficient data or statistics. But I have also heard him acknowledge on talk shows that the battle for same-sex marriage has already been won.'Climb up to the top of the hill and look down,' he said,'and you will see it coming. The vast majority of young people today are in favor of it and they are the future. Those are the facts, and we have to acknowledge them.'