German Shepards get a bad rep unfairly too so I would have expected you to be more understanding that breed doesn't equal bad temperament. I assume your dog wears a harness to warn others? If so then anyone letting their dog approach yours is incredibly wreckless.
Yes he wears a red warning harness. But people rarely see it or read it in time.
I think anyone letting a large powerful breed run free on public land is selfish because the dog will make other dog walkers anxious, upset people who fear or dislike dogs, risk barrelling into kids, cyclists and elderly people and knocking them over (even by accident eg chasing a ball). People should feel safe in public.
It’s reckless to let ANY breed off, unless they’re so well trained they walk to heel and recall instantly.
German shepherds have/had a bad rep but nothing like the bad rep of bull breeds. And not for temperament or dog aggression. They weren’t bred for fighting. They’ve never been used in dog fights so there’s no risk of illegal crossbreeding with pitbulls. Much of GSD bad rep comes from their use as police dogs and their wolf like appearance, and their tendency to become dominant if not trained well. I’ve always found them intelligent, affectionate, easy to train, good with kids but I’m aware of the breed characteristics as all owners are. They have a high prey drive for cats and squirrels (but so do many breeds). Like most working breeds they need a lot of walking and stimulation and can get destructive if not kept active, so I appreciate they’re not for everyone.
Mine doesn’t mind collies, at least he’s never reacted to one yet. But no collie has ever approached him aggressively or startled him. Collies tend to just walk past minding their own business IME.