Things might actually be worse in some respects. Security issues on airlines and such might be even more extreme in that circumstance. Although presumably things might be better for a lot of people outside the US.
It's possible, but I find it very doubtful that the increase in security measures would have been as severe, let alone more so. Comparing the reaction to the Oklahoma City bombing six years earlier, the difference is great enough that I suspect that a lot of the paranoia was fueled by the idea of an external enemy.
Personally, I suspect that if the 9/11 attacks had been domestic, the Department of Homeland Security most likely would not have been created.
Noah Millman wrote:
Link (which includes additional good retrospectives) thanks to Ampersand.
This article may have more political content than is suitable for LW-- if you'd rather discuss it elsewhere, I've linked it at my blog. I've posted about it here because it's an excellent example of updating and of recognizing motivated cognition even if well after the fact.