I know what yo mean- they are negative in the sense that they are not socially acceptable and they're a loss of emotional control, which is a valuable, socially constructive behaviour to have. But I don't see them as negative in a "deliberate" sense that needs reprimand, or explaination of why you shouldn't do it. I come from a perspective of teaching emotional control and communication as a way to avoid tantrums, rather than punishment such as withdrawal of attention.

I was thinking about our situation though and I do understand your point snacks. The ignore some of the random head-hitting my son does through the day as I think he is using it to get his way quickly and easily and if I respond to it all the time then I am teaching him that it's an effective way to communicate (ie. "rewarding the behaviour") so I am mindful of avoiding that.