Moore tugs at various others: cops, reporters, tv producers, etc on why we can't do stories about the cause of crime more than the crime itself. He takes a few tangential leaps here and there. But its still a valid point. Those not in the choir will miss this.
Now, where does Moore go wrong? Its a judgement call on how one would want to argue this, but the connection to the military-industrial complex is a bit overreaching (yet still well done), the aforementioned love affair with Canada (particularly the vantage points of the 3 kids outside of Taco Bell ... sure to win over nobody, but still good for a light chuckle here and there), as well as the history of US military intervention over the years leading up to the 9/11 attacks, complete with crash footage of the second plane hitting. All are basically points that Moore adds on in order to maximize the punch count, aiming for quantity over quality.
The Schoolhouse Rock meets Southpark intermission is a bit contrived, and aims at oversimplification. This is a snapshot of what some don't get about Moore's movies. This type of scene does not lay out the argument that Moore sets out to discuss. It caricatures it and pokes fun at the idea a little. What Matt Stone really thinks about guns in America (and yes, he is interviewed), I could care less. To whit, I can also add Marilyn Manson to that list (and yes, he too is interviewed).
By far, the single most dramatic moment of the entire movie is the footage of the Columbine shootings, complete with a few offings. It is, without a doubt, some of the most gripping movie viewing one can imagine ... all courtesy of simple security camera video feed. I would suspect that whatever reflections one felt about Columbine were quickly re-awakened and magnified during this footage.