I’m imagining the typical sci-fi situation where someone has a time machine, goes back to September 10, 2001, and tips off the Feds. Unlike the usual “don’t step on a bug and/or kill your grandpa” warnings, I can’t see any downside to changing history in this case. Al Qaeda and bin Laden would more than likely be contained. Bush would bumble along for eight (maybe four) more years pushing for tax cuts rather than war in Afghanistan and Iraq, since he wouldn’t have the juggernaut of 9/11 backing him. No Gitmo, no waterboarding, no dead soldiers, no galvanizing and empowering of the Right Wing, no yellow-spined Americans so scared of their own shadows they’re willing to shred the Bill of Rights. Yes, oh pessimists, bad stuff would still happen, but the evil, fear, and pain that spread as a result of that day is mind-boggling.