We are lucky that we have a troop in the area whos SM's son has aspergers, so he gladly runs the troop and takes in kids who need more attention/patience.
But its not just "special needs" kids that act this way. We have had kids in our cub scout den who have anger issues. One we worked with very closely, and he actually made an incredible positive change. He went from throwing scissors in his class at the teacher to actually saying yes sir and yes mam and listening to the adults after a year in the den. But we have others that don't respond so well and just have to sit out when they get out of control.
As stated above, we don't have degrees in mental health and are not properly trained to deal with these kids. And its especially unfair on our own kids if some kids take more attention/time away from their activities. That is why we just go with the sit out rule, if you cannot control yourself to participate, you need to go home or sit out the activity while the other kids are having fun.