PTSD is a label, but I dont' believe it's a negative label. Is that what you're asking? Is PTSD a negative, neutral, or positive label?

I actually wanted the diagnosis of PTSD, because the world would then make sense and my bad childhood would no longer feel like my fault.

I beleive that "Mentally Ill" is an incorrect and negative label for PTSD. Other negative labels to me are "messed up" "screwed up" "****ed in the head" "damaged" "crazy" "emo" "psycho" "nuts" "schizo" ... I could probably think of a few more with time.