I am cross-posting an e-mail I wrote to a friend who I discovered actually believe in the so-called “9-11 Truth” conspiracy:
I just wanted to make my case for why the 9-11 attacks were most certainly not a government conspiracy. There are lots of crimes that the Bush goons are responsible for, but a massive domestic terrorist attack isn’t one of them.
The arguments for a 9-11 conspiracy usually hang on two big logical fallacies (1) red herrings that prove nothing (dozens of Saudis including bin Laden relatives left the country after 9-11 without being questioned, so the Bushes must be behind it!); and (2) Offering up massive amounts of dubious evidence that proves nothing but is too voluminous to realistically respond to (to illustrate this, just look at the pro-conspiracy Loose Change documentary and then the lengthy sites like this one set up just to debunk stuff like that!).
There is a lot of good, concise writing on this that should set your fears of a government cover-up at ease.
The best I have read so far is this, showing how difficult such a plot would be to keep secret. There are so many interested parties, from fire fighters to the relatives of foreign businesspeople who became victims, who want to know what happened to their loved ones, from a number of different countries, and very few of whom have any reason to accept an alternate version of events. Not only that, if Bush’s political enemies had any credible evidence showing he is really such a despicable monster they’d be using it.
Of course you should also read through the 9-11 Commission Report (PDF). It is on the long side but is actually a very engaging read.
If you are going to take a class on government and politics, it is important to not be distracted by an inaccurate version of events. Conspiracy theories can be very compelling, but much like the stories of alien abduction and alternative therapies they shouldn’t really be taken seriously.
More generally, I would recommend taking a look at the site skeptoid.com, especially his pieces on critical thinking and logical fallacies (parts 1 and 2). I think you’ll find that seeing where conspiracy theorists go wrong is much more rewarding than subscribing to those theories yourself.