I agree with Judy Chrusch, I don't feel I have to explain to anyone why I wish for them not to pet MY pet. That irritates me beyond belief.
Would you allow a perfect stranger to drive your car, just because they like it or without permission, pick up your new born baby because they're cute? I wouldn't. It's no one's business why you don't want your pet to be bothered. Just politely ask that they don't and leave it at that. Judy said it correctly, socialization does not always mean direct contact. True, this breed may have a reputation, but the dog is still YOUR dog.