Lyric discussion by Snoardur 

The overall theme is obviously the ambiguous feeling of slavery and lack of purpose derived from contemporary life and work. Here's my take on it:

"I guess my birth left a great scar on my heart and mind"

The voice is pretty much saying that he was born "different"; he feels like he's permanently hurt emotionally and thus he will see the world in a different manner.

"Now I hand-pick cotton and struggle to sing "I am happy and I do what I like" But my voice breaks, and I start to hate my singing and simply everyone"

At some point he lies to himself saying that he is happy performing some purposeless and menial job-task, but then he sees reality and with it he hates his previous self-delusion; and everything and everyone that surrounds him.

"Mama told me be good, work hard, and love Mr. God Every Sunday, I lie, trying to realize why"

This pretty much confirms the previous: he discovers that the things he made himself believe are simply lies. Religious faith seems to be a common theme in the path to self-discovery: when one realizes that there is no such faith but only forced belief, and doubt hidden behind, despise and hatred commonly follow.

"I came to a standstill with lies and hopes inside my head Always seemed too late to turn and too soon to understand"

Then comes the point in life when not knowing what to believe, he feels stuck or lost, without a purpose or aim: lies surround him still, and delusional hopes are in his mind.

"I got used to spewing bile I wonder whether all those years hadn't been a waste of time"

Spewing disdain and hatred, despising everything: tormented by the thought of wasted time.

I guess that in the end, even if he says he can't complain, the voice seems restless: he knows that he is a free man, but somehow, the creeping feeling of being a slave overwhelms him, and thus he cannot enjoy life.

An error occured.