Conspiracy theories arise because governments lie so much and cover up so much. Or things happen afterward that make some people think there was a method behind the madness. A lot of seemingly dark things could probably be easily explained if government were open and honest, but that's not going to happen because other dark things would probably be proven true.
I think you really have something there. If government agencies didn't play politics so much and shared information they reasonably can in a straightforward fashion, they would make it much easier for people to trust them. At least since Vietnam it seems like my generation has not trusted what they're told by government agencies. And it would really help if the first reaction from every military and government agency wasn't to stonewall when challenged.
