It seems like te stupidest thing to me. Why are you going to attack someone who has politely asked you and/or your child to behave themselves or at least stop actively doing something harmful
Why the hell would they disincentivize their kids when someone has just given them an out to have a teachable moment and possibly nudge their kid behave better and possibly for the parent?
You answered your own question. They are crappy. When you identify how their kid is misbehaving it is a challenge to the parents.
Now a big part of this is how you couch and present your correction.