We aim at Iran because its government has, over a period of decades, carried out Acts Of War against this country and its civilians. Beginning with the Hostage crisis, on through the Beruit bombings, and multiple hijackings and murders.
As for the Saudis, we'll get to them. The oil shields them, for now. Besides, their government wasn't behind the 9-11 hijackers or al Quaeda, it was individual Saudis who financed those. Iran's government, on the other hand, directly carried out these Acts Of War as a matter of policy.
Are you telling me that the US soldiers are risking their lives in some act of ritual revenge? That sound policy and reason don't play a role any more? If old feuds and paybacks were the issue, we would be fighting in Vietnam now. And how come "the oil" shields Saudi? It only makes a more pressing target... Iran is not a Wahhaby country. They don't fund terrorists nor endorse their ideology. Saudi Arabia does both. This "matter of policy" is not clean. The clean solution is to destroy Radical Islam. Islamic Radicalism is worse than social radicalism (communism). It comes close to Nazism and should be swept clean from the face of the Earth. Starting with its source - Saudi Arabia.