This is why misanthropic Oscar, one of my favorites, was added. He was there to teach kids that people had radically different points of view. Oscar likes trash, worms, and being mean to people. Kids had to learn, and respect, that there were people like that in the world. Oscar, as nearly the only Sesame Street character who could get angry about anything, also served as a guide for children on how to manage negative emotions, both their own and other people's.
In the early 1980s, Will Lee, the man who played a character called Mr. Hooper on the show, died. Show runners consulted a battery of psychologists who specialized in grief counseling, and conducted studies to see if children could understand the concept of death and deal with it without trauma. Only after that did they go on to film the episode. They scheduled it to appear on Thanksgiving. This seems cruel to the kids, until you take into account that that was the day most likely for parents to be home with their kids, at which point it only seems cruel to the parents. The episode was well received, though, and the show hired other actors.
Link | Image: Children's Television Workshop