Not sure about 9/11, a lot of things seem suspicious. After all, it seems as if America broke Japanese codes relating to Pearl Harbor in '41 but allowed it to happen. It seems incredible that the US government would allow 9/11 to just 'happen'. Regardless of what I believe, I really, really hope they didn't!!!
JFK was IMO not shot by Oswald, lots of video footage shows Kennedy being hit from a completely different angle than where Oswald is supposed to have fired from. CIA hit most likely, possibly followed by the mob as Kennedy annoyed some Chicago mobsters I think it was.
As for conspiracy theories, I think more and more people believe in them. 'Official' versions of major events are often riddled with holes and contradictions that makes you wonder.
Now where did I leave my tin-foil hat