While there was a lot of spin after the fact by the Bush administration, the actual events were well witnessed, documented, and in my opinion, you'd be crazy to reject the overwhelming evidence that it was jihad motivated hijackers crashing a plane into a building. At least as far as the objective facts of what happened on the day, this is one of the very rare cases where you can take the US governments word at face value.
While my politics are very critical of power structures like the US government, I reject 'conspiracy theories' (a somewhat ill defined term) as irrational, dogmatic ("everyone else is a sheeple"), reactionary, and cognitively lazy. I wince when someone shares an Alex Jones video on facebook.
You don't need a conspiracy, governments have committed well documented atrocities.
This is just my opinion, conspiracies are dogmatic BS and are based around a perverse epistemological philosophy centered around making a point of rejecting the value of empirical evidence and falsifability