It would be nice if we could just leave them alone. Unfortunately they're always going to find something to want to kill us for. Pre 9/11 it was us having a few bases in SA. If it wasn't that it would be something else.
Maybe at the core it's jealousy of our affluence, or maybe it's religious. Who cares? The goal should be to reduce the number of innocents killed. What will accomplish that goal? It's clearly not the nice approach as we've seen in France and Belgium.
Pre-911 I would say the bases in SA, the war in Kuwait, our involvement in the Isreali\Palastinian situation, and of course our support for dictatorships or revolution depending on what time of day.
Anyways ever since our involvement in Iraq and Afghanistan their reach has expanded to the point the radicals are running a somewhat functional state across much of Iraq and Syria now. Talk about the worst possible result from our policies.