I had a woman in the woods round my house (where I walk ddog daily and never see a soul) pick up a giant fat Labrador when she saw my small border collie running up the path.
She screamed to me to recall ddog, which I did immediately, and she returned to me before going within 10 feet of the owner.
Other woman walked off with lab dangling from her arms, shouting that he was terrified now.
She did not have terrified dog on a lead at any time.
It looked very dangerous as the dog's legs were trailing, twisting it's spine. If my dog had been aggressive, she would have been able to attack the dog's legs and stomach and it would have been defenseless as it was being held.
I think if you have an aggressive or fearful dog, or one which has been attacked, and want to walk it around other dogs, you should use a yellow jacket or lead to indicate a nervous dog. Most dog will try to socialise with another dog, but if you clearly show your dog is nervous responsible dog owners will make the effort to avoid you, for your dogs sake and theirs.
Irresponsible dog owners will continue not to recall problem dogs, and daft owners will pick up normal dogs until they turn nervous, but you can't really do anything other than avoid them (or pick up your own dog and scream!)