A plus here means a good thing, an advantage, a benefit. Munger is saying that if we have learned a lesson from the events of September 11, 2001, that is a good thing, even though the events themselves were tragic. One meaning of intelligence is "the gathering or distribution of information, especially secret information." https://www.dictionary.com/browse/intelligence "Facing reality with more intelligence" means we should accept that more U.S. government resources should be devoted to gathering secret information.

I don't know who wrote this, it's not well-stated, but because Munger is a professor who teaches a class about 9/11, I believe that basically it means IF we are less weak, foolish or sloppy because of the terrorist events of Sept 11 (2001) that is good. (the "plus") "more intelligence" probably means more information from intelligence sources (FBI, CIA, Interpol, etc)

9/11 is about towers collapsing and more intelligence is about the best way to prevent a situation like that.

9/11 is about towers collapsing and more intelligence is about the best way to prevent a situation like that.

9/11 is about towers collapsing and more intelligence is about the best way to prevent a situation like that.