Oh, I understand completely what you're saying. But one of the many things that's enjoyable about Nip/Tuck for me is that at no time do I ever get the impression that we're being told how the characters are acting is the right thing to do - exactly the opposite, more than not. So I think the point of the particular disability they chose was to present a situation where clearly it wasn't a decision of major mental problems or something that might be seen as more clear-cut, and instead make a point about Sean, that he's unable to accept a child that's not "perfect." Which doesn't come as a huge surprise, actually, given not just his profession, but also how he reacted to finding out about Matt, and his real parentage. Sean has, as they say, big issues.