Ah, I gotcha. I do agree with the rest of your reasoning.

I've had this debate before (strangely enough, at a faith-based LGBT family meeting with leaders of the Willow Creek megachurch in Chicago), and that particular point has been a sore sticking point. In its weak form (as you've presented) it does nothing to address the matter of LGBT parents, and in its strong form (gay parents are worse), it contradicts pretty much all available evidence.