It's about energy geopolitics, resource scarcity, climate change and the coming resource wars with China and Russia.
Limiting the production of oil in Iraq strengths the price setting power of the Saudis and their American petroleum cohorts. This war certainly wasn't started because of WMD, the role of Iraqis in 09/11, or getting Bin Laden or even the fact that Sadaam killed his own citizens. He was tried for an act that happened decades ago. Why didn't we take him out during Desert Storm? If that was such a terrible act why didn't we remove him then? And don't feed me a line about foisting democracy on a culture that doesn't want it.