Here's why I think that Osama bin Laden worked for the CIA and that 9/11 wasn't merely a "they let it happen" thing:

• The government had been planning false flag operations using planes and bombs for decades (Operation Northwoods).

• FBI whistleblower Sibel Edmonds reported that the FBI was in constant contact with bin Laden.

• The US has a long history of working with Islamic terrorists, and the bin Laden family connections are well-known.

• Israeli spies were probably meeting with Mohammad Atta in Florida.

• Israeli spies likely occupied several floors of the WTC. Larry Silverstein rented them out at no cost, and they happened to be the floors that were hit.

• Saudi, Israeli, American, and Pakistani intelligence networks have collaborated for decades (The Safari Club).

And of course, the only way to do something right is to do it yourself. Waiting around for someone else to accidentally accomplish your greatest dreams for you seems like a bad bet. People don't have time for that shit; money was on the line.

I believe that the "they let it happen" angle is popular because it's a way for the mind to reconcile the coincidences of the event while still keeping OBL as the bad guy. Realizing that OBL was one of "our guys" is emotionally difficult and requires a major shift in worldview, but is functionally no more implausible or evil than the government just letting it happen.