COME ON BRO! You're thinking way too fuckin' basic here.
#1, who the hell would be threatened by a plastic knife? I have a hard enough time understanding why 45-95 people on a plane were too afraid of a real knife to rush the fuckers and overpower them. A plastic knife and take control of a 757/767?
#2, NO commercial pilot would EVER fly his own plane full of passengers into an occupied area or building knowing it would crash. I know several commercial pilots and none of them would do that...it's above their morals, ethics and basic human emotion. And certainly not against threat of a knife...or plastic knife!
#3, have you ever flown a commercial jet liner? It's not like driving a fucking go-kart, car or even a small plane. Flying a 767 at 250+ mph at low altitude and hitting a skyscraper takes a HIGHLY SKILLED PILOT...not to mention a pure madman.
This was no doubt a highly planned and orchestrated mass attack. It took extensive planning, skill and plenty of psychotics. The planes and routes were chosen, bypassing shitty FAA security, etc., etc. Knowing how to fly a commercial jet, turning off the transponder to avoid sending info to air-traffic control, plotting course and actually hitting a target.
It was a professional job...no if, ands or buts.