This is a point worth expanding. Gore Vidal in his novel "Kalki" written many years ago ends with the human race extinct -- the only living humans being a small group of men and infertile women. One member of the group breaks into the headquarters of various intelligence agencies to find out the "real truth" behind the murders of the Kennedys, MLK, etc.. This treated by Vidal as utterly trivial, and narrator never bothers to reveal to solutions any of these mysteries..
What the U.S. government does quite openly, with no attempt at concealment is far worse than most conspiracy theories. In addition there are the "open secrets" , murderous plots that are easily documented, and widely know, but are officially denied. For example the U.S. role in the overthrow of Allendes Chile, and the Indonesian invasion of East Timor; both denied at the time; both quite easily provable at the time ; both later admitted.
There are of course occasionally real conspiracies. But to try and explain the bulk of history by conspiracy is to deny that system is evil, to assert that evil occurs mostly through exceptional actions outside the system by a small minority of evil-doers.