Yeah I think this author is off on the timeframe. The late 70's/Earl 80's had some great cartoons. It wasn't until the late 80's/early 90's that cartoons had to have some kind of positive PC message.
It started with He-Man, When at the end one of the characters would come on and tell you the lesson you were supposed to have learned.
No he's got his time frame right on. Superfriends started in 1973, He-Man 1983. Maybe you managed to avoid the cruddy cartoons until the late 80s when they totally took over, but lame "moral lesson" oriented violenceless cartoons started taking over the industry in the late 70s. Don't forget the Smurfs (1981) probably the lamest cartoon ever with the lames "moral lessons" and most total lack of violence.
"Wheel of Morality, turn turn turn. Tell us the lesson that we should learn."
I think that the "edumacational" lesson at the end of GI Joe and He-Man were because there needed to be an "educational" component (something of "value") added on to what was a glorified toy commercial.