My take for what it's worth -
When we get really, really angry with someone, and we can't physically hurt them with blows, we try to hurt them with the meanest, nastiest, vilest words we can dredge up - the verbal equivalent of kicking the shit out of them.

Who among us has not said things we truly regret in the heat of anger?
Who among us has not lost it completely for a brief period and said extremely hateful things?

You certainly wouldn't expect it from a public figure, especially one who makes his living with words, and should know how to handle a heckler, but as we know, it can happen.

Atonement is in order.

Seamus