Why "Dark Poetry" is Perceived As "Deep"

I've often contemplated, as a poet, why poetry touching on emotions and subjects of sorrow, misery, anger, rage, despair and the vast variety of negative emotions are considered to possess "deep meaning."  As a child I believed these things were deeper, because happiness was a surface emotion that merely disguised the misery and suffering everyone must be enduring in what I felt was an purely cruel and unjust world.  Happy poetry, I felt, contained no substance.  It was merely fluff and nonsense.  Like writing an owner's manual that explained nothing.

I know this is not the truth.

Instead i propose the following explanation:

It's easier to find "depth" in sorrow and sadness and negative emotions, or at least to believe it exists there, because those emotions are dark, which is perceived as "deep".  They are often buried and confined, contained and hidden from view.  These emotions gather in the cavernous pits of our stomach and digestive tract, they cram tightly into knots along the our backs.  Tying us into heaps of useless meat, overcooked and fraught with senses of failure and powerlessness.

Poems that delve into those depths, that drag these emotions to the surface and illuminate them in the light of day or the brilliant flickering light of a candle are deep because they must be deep to reach their goal.  Like a deep sea adventure or a crazy dive into the uncharted paths of narrow and twisting caves, poems that struggle with what we struggle, are an adventure as much as the psyche can be an adventure.  Let's face it, the brain is such an incredibly complex mystery with deep fissures and folds, twists and turns like an impossible maze of hedges that we might never decipher. 

Light-hearted (happy) poetry can be deep as well.  I am not stating that happy poetry cannot contain profound observations on the human existence, profound observations that might strike chords with millions of readers, profound imagery that might brighten other people's lives or profound repetition of a word or phrase that hammers home a point that the writer is trying to express.

For some reason this entire stream of consciousness reminds me of a quote from the film "High Fidelity":

Was I depressed because I listened to pop music, or did I listen to pop music because I was depressed?

Alright, so it doesn't relate very well to my topic, but I'll be damned if I don't simply love that statement and see it as something profound in commentary about mass media, society, and culture.  As a poet, I wonder:  do I write depressing poetry because I'm depressed, or do I become depressed in order that I might create depressing poetry, because it is more readily and easily perceived as deep.