In p. 49 of this memento, the Rebbe is quoted as having written:
It is not advisable that people should be drawn in an intentionally non-realistic manner—very fat, with an overly enlarged nose, and the like—although they [the people who draw comics] have become accustomed to doing so. In my opinion, this is a great educational mistake, for with regard to children, the more simple and normal, the better. And in my opinion the same is true concerning adults. However, here is not the place to elaborate.
The explanation of the Rebbe’s view seems to be: When illustrations are unreal and fantastic, although they may be regarded as exciting, they are felt to be less personally relevant. However, when they are presented in a way that is realistic and normal, they have a real and lasting impact.