The theory that explosives were planted by the government in the towers is certainly one of the more extreme conspiracy theories. Just because that one may not be true doesn't mean you can write off all the other theories.
"I was surprised at the evidence that there were foreign governments involved in facilitating the activities of at least some of the terrorists in the United States... It will become public at some point when it's turned over to the archives, but that's 20 or 30 years from now."
- Senator Bob Graham, Chairman of the Senate Select Committee on Intelligence
http://www.thememoryhole.org/911/911-graham-admits.htm
And let's not forget that five members of Mossad (Israeli version of the CIA) were arrested just after the attacks when they were seen dancing in the street. That was on the news for the first day or two and then there was a sudden media blackout of the story.
http://whatreallyhappened.com/fiveisraelis.html