> Personally, I raise an eyebrow when a six year old boy raised by adoptive lesbians decides he is transexual, and I feel like society may be failing that boy.
This is a near perfect instance of xkcd's girls suck at math[1]. Shitty parents are tragically common, and we are failing children who are victims. But when a heterosexual couple destroys a child's life, we don't start talking about taking kids away from heterosexuals.
Also, I don't think polyamorous marriage is a good argument point against gay marriage. In time, as a society we'll see those opposed to the former as bigoted as well.
Anything that violates live and let live between consenting adults is on thin ice.