Don't you watch John Wayne movies?
They don't call them scatter guns for nothing and that is the reason they are illegal. Yes, if you are fighting a head on battle with someone then those that you hit are legitimate targets however, if anyone is even close to the action they are going to be hit or in danger of it, innocent or not. If maneuverability in tight quarters is the goal then the defender is more than adequate and the shot distribution is at least somewhat controllable by the shooter.