Forget about the term conspiracy. Would you subscribe to the possibility that the government has ever lied to you? That is all it comes down to. I normally subscribe that there are checks and balances to keep the government from lying to me. However, there comes a time that they tell you something you just can't digest as truth.
Tell me what you think happened to the pentagon strike during 9/11. Do you think that you have been told everything?
As with anything, a single lie manifests into more doubt.