There's a lot of darkness to Schultz that he deliberately played down, and a lot of it had to do with his frustrated desires to be a Walt Disney-esque media tycoon. The saga of his building a hockey rink and trying to attract a team to it in Northern California left him bitter and really angry, and finally he just gave up and gave the rights to his characters to Knotts Berry Farm.
Peanuts was pretty much dark across the board. In the late 90's, when Schultz finally allowed Charlie Brown to win at something (his first and only successful baseball game) it actually made headlines.