Judgement call
Although there were a few people who directly disagreed with what the man did, he was compelled to make a decision. Whether he did the correct thing or not — because it’s obvious that the boy didn’t learn his lesson — he was able to at least somewhat embarrass the kid who was being so discourteous.

Is this man’s defense a good one? Because he didn’t harm the kid, at least he won’t have many problems to deal with. Someone else remarked that, at the very least, he didn’t harm the child or else he would have a lot of issues on his hands.