I am terribly sorry if your experiences with ADD/ADHD have been so extreme. I can understand why you have your views.
While the cases you gave were sad, I think they are very extreme and rare cases. Most of the kids I know, or friends I knew in high school that were diagnosed with ADD had an inability to focus as their major symptom. I have many friends, and coach several kids that take Ritalin or Aderole (sp?). Oddly enough, I've never heard of ANY of them ever threatening to kill anyone.
I do know that sometimes kids with ADD/ADHD have other mental problems-maybe even caused by the symptoms of ADD/ADHD. Perhaps you are confusing things.