According to Administration and military officials, the President "insisted" that the team that took down bin Laden had to be big enough "to fight its way out of Pakistan if confronted by hostile local police officers and troops."
In other words, if the Pakistani army or local police found out about Operation Geronimo, the United States would have ground troops in Pakistan firing against their army. Considering that not even the Pakistani government knew about the raid, much less the army or local police force, the chances of this occurring were relatively high.
If this had indeed happened, it would have lead to a debacle of huge proportions. If the United States had killed bin Laden and then had to kill dozens of Pakistanis, much of the nation of Pakistan would likely be calling for war. This easily could have gotten every single US Seal killed and could have killed dozens, if not hundreds, of civilians in the densely populated city of Abbottabad.
In a worse scenario, which was also very likely to take place, the Pakistani army might have noticed the helicopters and Navy Seals long before they reached bin Laden's lair. If that happened, not only would Osama bin Laden still likely be alive, but the United States would have likely been engaged in a firefight with Pakistan, likely killing dozens and completely missing out target.
Consider, for a moment, that our relations with Pakistan are strained as it is. And the mission was a success, with no civilians and no Seals killed. Imagine dozens dead, a firefight on the ground in Pakistan, miles from the Afghanistan border, and Osama bin Laden getting away alive.
The NY Times continues:
Mr. Obama’s decision to increase the size of the force sent into Pakistan shows that he was willing to risk a military confrontation with a close ally in order to capture or kill the leader of Al Qaeda.
Such a fight would have set off an even larger breach with the Pakistanis than has taken place since officials in Islamabad learned that helicopters filled with members of a Navy Seals team had flown undetected into one of their cities, and burst into a compound where Bin Laden was hiding.
One senior Obama administration official, pressed on the rules of engagement for one of the riskiest clandestine operations attempted by the C.I.A. and the military’s Joint Special Operations Command in many years, said: “Their instructions were to avoid any confrontation if at all possible. But if they had to return fire to get out, they were authorized to do it.”