[Chris O'Carroll]

One crucial consideration, I think, is that comedy is not the opposite of seriousness. Comedy is a mode of seriousness. For example, in literature and in life, sex and death are two of the things we take most seriously, and also two of the things that are most likely to crack us up. The speaker in "To His Coy Mistress" is dead serious about wanting to get laid, but it's inconceivable that Marvell wasn't smart enough to know what a funny poem he was writing. The Porter scene in Macbeth and the Gravedigger scene in Hamlet are usually referred to as "comic relief." And it's true that they do give the audience (and the actors) a break from high-tragic emoting. But they also serve to highlight the tragedy. A comic scene about mortality in Hamlet, a comic scene about damnation in Macbeth -- there's more than just "relief" happening there. And don't get me started on the Fool in Lear.

Some light verse has exclusively or primarily entertainment value, while some has a more serious intellectual, philosophical, or social commentary agenda. Edward Lear and Ogden Nash vs Lewis Carroll and Dorothy Parker, perhaps? Both kinds are "serious" as well as "light," but the seriousness of the former has to do more with elegant craft than with surreptitiously weighty content.

(Lite verse is a different matter. There's plenty of earnest greeting card doggerel that emphatically is not trying to be funny, and that no intelligent reader can possibly take seriously.)