If you talk down to your target audience, inferring they're stupid, does your audience get it?
This comic is from an old Teen from the mid-1960s. In order for there to be humor a teenage girl would have had to recognize that someone is stupid. I'm guessing it was hoped that the reader would not identify themselves as the target, but would instead think, "Oh yeah, Margie is just like that!"
So why would editorial think this was funny? Am I reading too much into this? Hey, it's late and my net access has been out all day.