Crappy dog owners = crappy dogs. I too have had that experience. My pooches are in my control. If there is something that may distract them, I tie them up. Dogs owners need to pay attention to changing conditions. If a group of people show up with dogs, then your dog will get curious.
If however somebody wacks my dog and my dog didn't do anything, I will wack them back.
Another thing dog owner needs to avoid is bringing too many dogs. A river group is great with one or two, but three or more seem to be too hard to contain. I feel the same way about people.