Welcome to the madness!
The people of Afghanistan can decide if they want to harbor Al Queda in their country. And, in fact, many of them DO want to. They consider Bin Laden a hero. By doing so, they are putting themselves in harm's way, because we have a right to defend ourselves. The alternative is for them to say that 9/11 was a horrible thing and that they do not want any part of it. Don't provide safe harbor to those that would work toward another 9/11 plot.
Sure, but now put the US in every place you mentioned Afghanistan, put US military where you mentioned Bin Laden, and put any number of mid-east invasions and bombings and drone strikes and sanctions and etc where you mentioned 9/11 and see if it doesn't ring just a little true.