I judge when there is no reason for it. And except for clearing tubes i am yet to hear a good reason to give a young child coke. Even sips imo are bad because you are just allowing them to taste something they shouldn't consume, or want to drink. There are so many reasons why coke is bad for a child that I am not sure why any parent would bother.
I am going to be controversial and say I don't think diabetes is a good enough reason either sorry. I have nannied children and had people in my family as children and a friend all with diabetes, none of them "needed" diet drinks as treats, just like every other child doesn't need a treat a day or meal, or even at a special function etc. I am saying this specifically because in DH's family there are young children with diabetes who have huge jugs of diet coke at every family function like it is water, because "they need it" to feel ok, or involved or like it is a party for them as well. It just isn't needed and it is damaging.
ETA not commenting on hypo situations, more people who give it as a sugar free/carb free treat for very young children. Although in a hypo you could give other things, not coke so I still don't see the need.