Why do some actually believe Glenn Beck tells the truth?

Because they are extremely gullible idiots who believe whatever Fox and Beck and Limbaugh sells them. They DON'T do any research on their own. They put their total faith in those people's hands. If Fox tells them tomorrow that the sky is falling, they will all run out and buy umbrella hats. Beck also tried to commit suicide. That should tell you something about his stability, or LACK of lol.