From Michael Scwartz:

God knows the Vietnamese people had justification to strike back at the United States during the American War in Viet Nam.  The death and destruction visited on that small nation has been well documented, and yet, there was never any Vietnamese-sponsored terrorism in the U.S. between 1945 (when American advisors first entered the country) and 1975 (the final victory of the NLF).  I was thinking about parallels between the Vietnamese and the Palestinians, and it occurred to me that maybe the reason the Vietnamese resistance did not engage in U.S.-based terror (aside from the logistics, materiel, and manpower) was the existence of a strong and vocal antiwar movement.  The space for political discourse was boiling over with powerful and consistent voices against the war, and it would have been counterproductive to the Vietnamese had they blown up buildings and killed Americans here at home. 

The Palestinians, on the other hand, must feel that all of America does not care about their predicament.  There are little or no voices raised in protest of the Israeli occupation.  There's no discourse against the use of American weaponry to kill, maim and wound Palestinians.  Maybe, as Hannah Arendt said, the lack of politics on the part of the American left vis-a-vis the Israeli-Palestinian struggle has led to a vacuum, tragically filled by the bin Laden bombers.  Maybe the left needs to look at why it hasn't been more supportive of the Palestinians' right to a state of their own and an end to the occupation that is destroying their hopes and dreams for the future.  Maybe, had the left been more active and vocal, the bombers would have felt constrained to stay their hand.

I don't know. 

Just a thought.