I'm distinguishing between something being "wrong" vs. something being "acceptable." Wrongness to me is a moral attribute; whether something is acceptable is a purely subjective and individual quality. Maybe the tantrum is unacceptable to us and to nearly every other adult in human society, but it's still subjective. I think that parents absolutely should show with their actions and words whether something is acceptable _to them_ and give advice about what will be acceptable to others (they will learn soon enough anyway). That's what GP did by showing that throwing a tantrum was an unacceptable way to get ice cream.
The key part is that he didn't then go on to say/communicate "and what you're doing is wrong and you should be ashamed of yourself," or something to that effect. The exact words don't matter, kids internalize shame very easily: if you think it's wrong or shameful, then they will get the point. It will be effective at preventing the behavior in the future, but damn, shame is like the nuclear option in my opinion when it comes to parenting. Obviously there's a healthy amount of shame that we should all have for things that are genuinely shameful. But is there really anything shameful or wrong about a lack of emotional control? The child is a child, they don't know any better.
So the question is what is unacceptable? I would argue that the tantrum itself is totally acceptable, assuming (as GP has said in follow-up comments) that it's a safe space for the child and the parent has the capacity in that moment to hold emotional space for the child. I would even argue that although the tantrum is obnoxious, the part of the tantrum where the parent says "yes, it's good to express and vent your anger"--even more so for a girl in a world where girls are told not to show anger--is downright healthy. The part that's totally unacceptable, in my opinion, is the idea that the anger will get her the ice cream. But if you say "not only will you not get this ice cream, but also you're not allowed to throw a tantrum ever because it's wrong," that kid will more likely than not internalize a certain amount of shame for her actions, and next time she wants to express anger she will feel ashamed about it. Which sucks, because that stuff, built up over time, will stick with you well into adulthood. Hence the therapist :-).
I'm distinguishing between something being "wrong" vs. something being "acceptable." Wrongness to me is a moral attribute; whether something is acceptable is a purely subjective and individual quality. Maybe the tantrum is unacceptable to us and to nearly every other adult in human society, but it's still subjective. I think that parents absolutely should show with their actions and words whether something is acceptable _to them_ and give advice about what will be acceptable to others (they will learn soon enough anyway). That's what GP did by showing that throwing a tantrum was an unacceptable way to get ice cream.
The key part is that he didn't then go on to say/communicate "and what you're doing is wrong and you should be ashamed of yourself," or something to that effect. The exact words don't matter, kids internalize shame very easily: if you think it's wrong or shameful, then they will get the point. It will be effective at preventing the behavior in the future, but damn, shame is like the nuclear option in my opinion when it comes to parenting. Obviously there's a healthy amount of shame that we should all have for things that are genuinely shameful. But is there really anything shameful or wrong about a lack of emotional control? The child is a child, they don't know any better.
So the question is what is unacceptable? I would argue that the tantrum itself is totally acceptable, assuming (as GP has said in follow-up comments) that it's a safe space for the child and the parent has the capacity in that moment to hold emotional space for the child. I would even argue that although the tantrum is obnoxious, the part of the tantrum where the parent says "yes, it's good to express and vent your anger"--even more so for a girl in a world where girls are told not to show anger--is downright healthy. The part that's totally unacceptable, in my opinion, is the idea that the anger will get her the ice cream. But if you say "not only will you not get this ice cream, but also you're not allowed to throw a tantrum ever because it's wrong," that kid will more likely than not internalize a certain amount of shame for her actions, and next time she wants to express anger she will feel ashamed about it. Which sucks, because that stuff, built up over time, will stick with you well into adulthood. Hence the therapist :-).