One of the scariest songs ever written is Tom Waits' bleak 'God's Away On Business'.
Seeing the Sesame Streets puppets singing it makes it even worse. But at least it introduces the kids to the idea that the universe is an arbitrary concoction indifferent to the activities of bipedal carbon-based life forms (who's in charge in God's absence? 'Killers, thieves and lawyers'). I had a friend who used to cry when I outlined this world-view. Ah well.
Mind you, there's always been a streak of savage violence to Kermit, as these early adverts show: