Of course, most modern poetry flouts decorum, flaunts its lack of decorum or fittingness. Yet doesn't the ability to recognize incongruity depend on a notion of congruity in the first place? In other words, we cannot get an effect of incongruity until we notice that something seems "wrong." We also have to feel that this "wrongness" is "right" in its context, that it works and is not simply a mistake:

The right notes.
The wrong wrong notes.
The right wrong notes.

***

The problem is not "not taking poetry 'seriously.'" After all, one could take poetry very seriously indeed yet have no ear, no eye, no notion of what poetry is. Earnest but misguided. Pompous and grave. Or one could seem to take poetry more casually yet actually take the serious part of poetry more seriously. What is the opposite of serious in this case? It is not the comic nor the casual. The only word I can come up with is "Pinsky": the wrong kind of seriousness can be much worse than a sense of unseriousness.