Just as it's ridiculous to suggest that fast food is the only driver of the obesity epidemic, I also believe that the numbers prove that it is one of the largest contributing factors. However, there's really no substantive difference between fast food and the processed foods located in the center of the supermarket. They're made of a bunch of crap and they've been cooked until they only superficially resemble food. Actual food has things like enzymes in it, and if it includes something like corn syrup it's not being used in place of vegetable oil and the flavor balanced with citric acid.
Also, you're glossing over the role that eating out in a typical restaurant in America plays, which has been discussed above in this thread. Most restaurants serve portions which are very large when compared to the actual caloric requirements of the average American; I'm not necessarily complaining, because I too prefer to have more food than I will eat than to go hungry at the end of the meal, especially when I'm paying any significant amount of money. The margins on food service have only become slimmer in recent years. Unfortunately, we have a tendency (whether learned or inherited) to clean our plates, so these two drives are somewhat problematic.
In summary, the argument was not solely about fast food, but it's clear that a large portion of the blame can be laid there.