Kicking someone when they are down does not necessarily arise from evil or selfish intentions.  In fact, it may arise from very good, nay altruistic, intentions.  Normally people are so full of themselves that it is next to impossible to arouse them out of their dogmatic slumber by a well-intentioned kick, that is, criticism of even the most constructive kind, the kind that tries to help the other person help themselves.  If, on the other hand, the person is already down from having received a kick from someone else, this may be the best time to state or reiterate the constructive criticism, because the person is “prone” to accept, at such a juncture, that he or she is less than perfect.  If, for instance, someone has been chastised at some public forum, this may be the best time to get through to the person with oft-reiterated criticism, and to have a realistic hope that the person would agree to fundamental reforms that would have been considered out of the question before.