"Anthropogenic Global Climate Change", previously known as "Global Warming" (and "The Coming Ice Age" before that) is one prime example of a conspiracy theory that even many otherwise skeptical people push. It doesn't hold up to scrutiny, no matter how brilliant the minds are that promote it.
Basically what it comes down to is that you and I are destroying the planet by not living a primitive life, and whatever fear can be generated, (using warming, cooling, drought, floods, disease, or extinctions) in order to scare you and me into accepting government regulation of our behavior, will be grasped and used as a psychological weapon.
The State is another conspiracy theory I don't buy into. To imagine that people can't run their own lives as well as, or better than, random (and distant) strangers is insane. To imagine that theft, murder, kidnapping, rape, counterfeiting, and various other wrong acts are OK as long as they are done by people who were elected to do those things, or their employees, doesn't make any sense.
The humorous thing is that the proponents of both of these call the people who don't buy into the conspiracy theory names to try to invalidate the true skeptical position. Don't let them get to you. Liberty is right.