Skepticism and conspiracy theory-ing are not the same thing. It's the difference between wondering and making bold statements.
Wondering if there was something more to 9-11 (ie. the government allowing the attacks to happen, whatever) is one thing. As long as it's just "wondering," it's fine. And if actual evidence actually comes out to support that view, then it's not a conspiracy theory, but actual fact.
However, making definitive statements, like, "it was faked" is stupid because there's no real evidence existing for that. The latter is what the point of the topic is, and it mostly comes from people with a lack of success attempting to build their ego in other ways.