Please do not take this as a lecture.
Your post was thoughtful and I wanted to comment on this one point. I would ask that you and others reconsider the use of "you must be adopted" or "what are you.....adopted?" etc., to illustrate that someone is different or other than normal. I cringe every time I hear someone say that and hope my child is not within earshot. I don't lecture them, because they are making the remark innocently enough. It's just something our culture does. But it's something I believe our culture should rethink. It reinforces a negative stereotype whether people mean it or not. It says that adopted people are different and don't fit. Is that the message we want to send? Especially to children? So to those who toss this phrase around, please think about how it might sound to an adopted child's ears, because if you use it at home, your children WILL repeat it out in the world.
This is not directed at you, but is a comment in general. I realized last night that what is most bothersome to me may not even be the movie line, "He's adopted," but the audience reaction.
Why does that line cause such laughter? Because it plays to every stereotype and prejudice our society has regarding adoption. The laughter is the part that probably would hurt kids the most. Because to them, it feels as if the crowd is laughing AT THEM, on some level. At the core of who they are. And that can be painful. More than that, it makes me wonder why adoption as the explanation/excuse for a character's (major) flaws is such a cause for laughter.