Lawrence Korb summarizes the arguments for a responsible exit from Iraq at the end of the year, contrary to the wishes of the military establishment in the Obama Administration.

if US troops remain, violence against Americans may increase and Maliki’s government will likely collapse. Muqtada Al-Sadr, whose support was critical to Maliki’s success in forming a government even though he finished second in the elections, will likely withdraw his support from Maliki if he renegotiates the agreement, thus creating political chaos. In addition, he has promised to reconstitute his Mahdi Army militia, which could be joined by other Shi’ite extremist groups in attacking Americans.

…the Iraqi security forces do not need us. They already outnumber the remaining insurgents, and their counterterrorism units are first-rate. Although they are not yet ready to repel an invasion by a foreign government, there is little likelihood of that happening. Even Iran does not have to invade Iraq to have influence there. It was the Iranians who got Al-Sadr to support Maliki. And Maliki has repaid them by supporting their positions on Bahrain, Lebanon, and Hamas.

…just as the invasion of 2003 undermined the overall strategic interests of the United States, so too will keeping forces in Iraq beyond the agreed-upon date. It will enhance the Al Qaeda narrative about American intentions in the region and also make it impossible to get a negotiated settlement in Afghanistan. Remember Al Qaeda was not in Iraq until after the invasion and occupation and will likely come back in large numbers if we stay. Moreover, the Taliban will never accept a negotiated settlement with the Karzai government in Afghanistan if they do not trust us to leave that country at a date certain. Giving priority to Iraq over Afghanistan in 2003 undermined our interests by creating a quagmire in that country. Having troops in Iraq would do that again.

I’ll give you two more reasons, buried inside this WaPo article noting that April was the deadliest month for US troops since 2009, with 11 military deaths. First, we have the uptick in mortar attacks against US bases. The point of an extended US military presence, according to those who want it, is to stop sectarian attacks among Iraqis. But many of the attacks target the occupiers:

Some U.S. service members say they have sensed a surge in mortar attacks on U.S. bases in the south amid the mounting political pressure in Baghdad for a decision on the deadline.

This week, warning sirens sounded on the U.S. base in the southern port city of Basra when mortar fire struck the airfield, not far from the building that is expected to be turned over to the State Department later this year for use as a consulate.

An announcement of an extension to the US presence will not only lead to the dissolution of the Maliki government, but intensify attacks directly on US personnel. Service members will die, and the purpose of that spilled blood is inscrutable. And the US would take the position of Hosni Mubarak with a mass popular movement arrayed against them, demanding that they exit.

The second reason to leave on schedule is that the uncertainty around leaving is being used as a political football by the minority Sunnis. This is the next-to-last paragraph of that WaPo article:

Iraqi Prime Minister Nouri al-Maliki has said that Iraqi forces are capable of managing the country’s security and that it will not be necessary for U.S. troops to stay. But after the Sunni parliament speaker said this week that the legislature might debate reaching a decision of its own, Maliki said he would hold multiparty discussions on the issue when he returns from a trade mission next week.

The Sunnis know that Maliki would have all kinds of problems keeping the government together if he asks the Americans to stay. So they want to force his hand. It’s a two-pronged assault, with US officials and Sunni lawmakers pressuring Maliki from one side, and the Sadrists pressuring him from the other. There’s evidence that he’s already cracking under that pressure. This week, Iraqi security forces opened fire on peaceful protesters in Mosul, who rallied against any extension of the US presence.

I’m not even getting into how this broken promise would impact the dynamic of the 2012 Presidential race. Within Iraq itself, extending the military presence would cause complete chaos, and make Iraq far more unstable than whatever problems that presence would seek to solve.