Maybe having a reason can lead to complacency, but is a person like that going to be a huge success otherwise? With the right attitude, having a reason can lead to better understanding, greater drive, more success.
I don't think it's about having a label. It's about understanding what's going on so you can better accommodate it. Once you have a diagnosis, you automatically have access to a vast wealth of knowledge which can help you to cope.
Think of breaking your leg. Is getting it diagnosed as "broken leg" just a search for a label which will lead to complacency? Are you better off thinking your broken leg is an eccentricity which is some unique part of who you are? Of course not, you want to get it diagnosed as "broken leg" so you can bring all modern medical science to bear on it and get it fixed up so you can heal, and cope with it in the meantime.
Mental disorders are not the same as a broken leg, but they aren't so different, either. I think we'd be better off if we'd stop drawing this fairly arbitrary line between "physical" and "mental" problems.