1. There is no such thing as reading into stuff too much. Only incorrectly making conclusions from what you have observed.
2. I think that is a bit of an oversimplification of what the episode is about… Most South Park episodes are actually rather brilliant thematically and have multiple messages - and no, I’m not looking too far into it. It’s actually rather exciting to dissect a South Park episode.
One of the themes is that what was offensive when the book was made is unoffensive now, signalling the internal freedom we have to say and think certain things that we didn’t before. Another is how susceptible to suggestion some people can be (Butters planning to kill John Lennon and Ronald Reagan). There are more than a few things that episode is about, as with any and all South Park episodes (I’m just going from memory, otherwise I’d dissect the entire thing).
The funny thing is that “don’t read into what isn’t there” actually is one of the themes, but they themselves write in a style in which they wish to say a lot more than they actually do. They contradict themselves in that episode, as they usually want people to read into things. That is often their point, even. You can find message in the most odd and non-sequitur of things; I try to include message in everything I do, sometimes more subtle than others. Even when I do something utterly “random” (I use quotes because if something is created, it isn’t random) I try to include something that is aware in some way, like Pepper Spray Cop and Rick Perry in Arrow in The Knee.
That episode is completely brilliant, though. The books written make me laugh harder than probably just about anything else. When poop comes out of his nipples, I just die laughing.