The fairground "petting zoos" with the ponies hitched to a sort of merry-go-round thing made me feel sad, like they were just cogs in a machine.
The barn I ride at does pony parties. They are pre-scheduled and time limited, either held at the barn or at the partier's home. They have an assortment of ponies, but usually bring one of the horses as well because the adults eventually give in to the excitement and want to ride, too. Usually there's two or three handlers and the ponies can have as much attention as they like.
When not working, the ponies have turnout and care just like all the other horses. That seems just as reasonable to me as horses for lessons and trails, as long as they're of suitable temperament.