My child's health history is not the concern of every person under the sun. They do not get to ask what the dog does, what's "wrong" with my kid, how long it took to train him, how much a SD costs, what breed he is, what his name is, if they can have a picture, etc.
I had a guy at a Kidcot station crawl under the table to pet the dog. A grown man, crawling under a table to pet him. I was not polite to him in the least (I normally at least try). I've also had one woman insist that she MUST have a picture of him and ask me if I would mind posing him. Uh, you want a picture of a posing dog, Pluto is inside the park.
On the other hand, I was waiting for the jungle cruise in MK one day and the cast member kept looking at him and you could tell he was insane with desire to just pet him. He never asked, he never made a single comment other than "he's pretty." When we were about to board, I asked if he would like to pet him, and of course he jumped at the chance.
I let kids at times, mostly just so he gets practice on the command! Normally on the monorail ride home at night I'll take his vest off (especially if there are kids in the car) and let him be a dog. And yes, there is a significant personality change when a dog's vest comes off! He LOVES the monorail ride home with his vest off, he gets to pet everyone!