Yeah, we're about to get heady.
There are some definite class distinctions going on in Bartholomew. While the royal bell ringer and the royal trumpeter may have been bumbly and clueless, they could see that the oobleck was a problem. The Captain of the Guards, on the other hand, who is much more of an aristocrat, is another version of the King. He's just as prideful—heck, the man is combing his handsome moustache when we meet him, and just look at the way his chest is all stuck out. And, like the King, he does the stupidest thing possible: he eats the oobleck.
Now, we don't know if this was intentional or not, but it seems like the problem with aristocratic adults is that they're so blinded by their own pride and ego they don't realize how incompetent they are. The lower classes, on the other hand, are more down-to-earth with their incompetence. At the very least, Seuss is highlighting the more absurd aspects of entrenched power structures.
How's that for some light kids' reading before bed?