HUH? I didn't say "disengage from the world". What I suggested is that we DON'T LET THE BAD GUYS INTO THE COUNTRY IN THE FIRST PLACE".
It is not "shortsighted" at all, and a pretty simple premise: if you export the bad guys (round them up, like we did the Germans in WWII that were sent here by Hitler to blow up US factories during the war), and have a preventative mechanism in place to keep them from coming back (good border control), they can't hit you. Or, at the very least, you make it VERY hard to attack the US from within.
As it stands today, ANY terrorist could walk ANY weapon into the US and detonate it at will. If we keep them OFF US Soil in the first place, or make it a LOT harder, this is a whole lot less likely to happen.
We are "sitting ducks" as it stands now, and lack the societal awareness/intelligence and political will to do a darn thing about it.
Excuse me if I presume something thats untrue. Ive found that virtually everyone who promotes hermetically sealed borders imagines it as part of a disengaged foreign policy, abandoning relationships with states like Saudi Arabia, Egypt, Pakistan etc with mixed cooperation on terrorism.