i remember watching that particular Simpsons episode when it aired back when i was in sixth grade. it's alot funnier now. back then i think i used it to form my political views but i can't exactly remember.
anyway. maybe it's argueing that we're all stupid. maybe it's argueing that if we don't watch out evil aliens are going to take over. all of which could be very true but i think it's all in good humor. and it's what the simpson's does best. but that's just my opinion.