This is a tough situation. I'm going to go out on a philosophical limb and say that I can understand both sides of the story. On the one hand, families with autistic children deserve to go out and enjoy the fruits of our cultural stew just as much as a family of NT's does. In family restaurants, you can be sure that there's going to be kids yelling and whatnot. It would be more appropriate at a McDonald's than at the Olive Garden, but I digress. Most families will tend to a screaming kid by removing them from the dining area and maybe getting them outside to calm down. Nobody objects to a child getting upset. What most people object to is when the kid continues to scream and carry on throughout the entire meal, and while the kid's parents completely tune it out, everybody else is uncomfortable and can't wait to leave. When that happens to me, I get annoyed and feel like I just paid a lot of money to eat right at the screaming kid's house. It almost feels invasive to me to have to put up with it past a certain point.
This can happen with NT children in which they're allowed to act however they want in public. Maybe I'm being an old lady here, but letting a child do whatever they want in a public place, and not teaching them proper social behavior, is not doing the kid any favors.
Having worked with autistic / mentally ret*d individuals, I have seen way too many parents who let their autistic children go absolutely bonkers in public places. For the severely autistic, there really isn't much they can do about it. However, for lots of the autistics, and especially for aspies, it is entirely possible for them to be taught the proper way to behave around others in public. If they are unable to learn, perhaps the parent is amiss for making them be in a situation that they cannot handle, hence the bad behavior. I can understand a meltdown at the grocery store or Wal Mart, because sometimes the child has to go to the store with their caregiver, and sometimes it's too much. However, a restaurant meal is a luxury treat (don't believe me? Just look at your bill next time!), and people pay good money for these meals. Why, if you are the parents of an autistic child who cannot behave in public, would you put your child in such a situation? Perhaps waiting until the child is older and better able to handle social situations would be smarter than "forcing" them on a mostly unfriendly world.
With all that being said, there is NEVER a reason for violence in a case like this. The attacker should be prosecuted to the fullest extent of the law. If the attacker had any brains, he would have talked it out with the manager of the restaurant and perhaps have gotten a free meal out of the situation. Instead, he acted like an irate gorilla who's banana was taken away.
As for the diners who said they "weren't bothered" by the child, maybe they weren't, or maybe they were, but felt that they had to stand up for the family who had been attacked. It is entirely possible that the attacker has psychological issues and took it out on the father of the autistic boy. Since I wasn't there, I'll have to go with what the news article said.