I'm skeptical of most conspiracy theories. The only one I have any real belief in is a conspiracy between Big Oil and the Auto industry.

Anyway, here are two good (and funny) reasons why a lot of conspiracies don't make sense (especially all the 9/11 ones out there):

Official Website for the Titanic truth movement.

and don't forget this one:

There is no 9/11 conspiracy you morons.

Enough said.