Although I don't agree with a 'damn good whacking' I do agree with your post in essence. I am a teacher and I have had several children with ADHD. In my experience you get the parents to change their diet and set some boundaries at home, you set the same boundaries at school and you get a child who begins to understand that actually... they don't rule the roost.
You definately raise a valid point. The behaviour these children display, in comparison to their peers, shows they have no boundaries. They are used to getting their own way and will completely flip out if they don't. ADHD may well be a condition but after 12 years of teaching I can honestly say I have never had a child diagnosed with ADHD that HASN'T improved after these boundaries have been set.
For some parents, giving a child a label is as good as saying 'oh he has ADHD, just ignore him' when it is the opposite that is needed.
In my opinion of course...