And if we had never had a continuing presence there in the first place? Why did we go to Iraq in the early 90s? What other battles and wars beforehand we were part of? Why did we go to Mogadishu?
Another 9/11 or worse may have occurred. Something that forced to go back certainly would have.
There is easy answer to Islamic terrorism. Islam is a religion of conquest and has been since its inception.
Radicals will always hate the US because it isn't Islamic, because it is aligned with Israel, or in the case of the Shiites, because we align with the SAudis.