I wouldn't really read too much into this film and create fantastic metaphors, ie. its an allegory of the war in Iraq or whether the oil miner (Daniel Plainview played by Daniel Day Lewis) is supposed to represent Bush or Osama. Its basically a story of a strong willed man who is determined and extremely competitive than it causes him to go basically nuts after a period of time. Maybe its a commentary on the American Dream. If there's a morale to this story its this: getting material wealth, doesn't make you fulfilled; that was the main goal of Plainview - to strike it rich and to build a big house for his children to play in.
The only thing that keeps him relatively sane and humane - was the love for his only son. There are many moments where this is displayed, esp. the moment where he left his son on the train and walked away, hunched, and in great emotional pain.
His love for his son is one of the reasons why the powerful tirade that Plainview gives at the end - where he disowns him - is so painful to watch. If he didn't care for his son, if they didn't have such an emotional bond, that scene at the end wouldn't have meant much.
Plainview isn't a monster, he even cares for the daughter of the farm owner - and told the latter off for beating her up for minor infractions- who later gives him a moving hug at his baptism. (His defense of the young girl makes an interesting juxtaposition to the meeting with the other Standard Oil lawyer- where the latter made a condescending remark about Plainview's family during negotiations that enraged the miner.)
Plainview got ALL he planned for. A huge oil mine, massive wealth, beating the the megacorp Standard Oil and Railroad Trusts, a beautiful mansion by the sea, and triumph over his "enemies". But along the way, he somehow alienated his own son and turned into a cold blooded murderer - not to mention a crazy drunk.
However, as he admitted to his "brother", he had an extremely competitive spirit. He badly wanted to win and he hated seeing other people succeed. He especially wanted to humiliate people who got the better of him, esp. the preacher Ely and the Standard Oil.
It is this competitive selfish spirit that drove him to hate his son and to despise his love for him. Love can be a very humbling experience as you are giving something of yourself to another person, it is an unselfish act. However, that love detracted from his main goal: making oil, making money. And in the end, his goal consumed him utterly and horribly.
Even after he had made it all - he just couldn't let go.
Powerful performances by Daniel Day Lewis.
Its worth watching for this reason. I was particularly moved by DDLewis' performance as he reminds me a lot of my own father, a strong willed man with iron willed determination yet with the capacity for great affection.
On the mirror image side, there's the pentecostal preacher, Ely, who is deluded and whose behavior mirrors the crazy obsession and determination that Plainview has. Notice the attack on his own father whom he curses and physically assaults.