After re watching this documentary i think its safe to assume the drugs help to disconnect kids from emotions/others/themselves and consequences of their actions. It seems to be an "easy option" (as admitted by one of the Doctors in the documentary) that parents are more willing to take rather than traditional behaviour modification techniques.
I also think your points are valid, without a doubt. Still, it would have to be judged on an individual basis, and there is also the view that their suppressed emotions for a time may be a good thing. It may make them less likely to act due to anger or any other emotion.
I still believe that we don't know enough about the subject to judge it definitively one way or another. Me, you, or the medical professionals.