A generally unsubstantiated claim - generally based on what is called an argument from ignorance, linking completely unrelated things, etc - that is usually considered to be against the well-being of the demographic of the conspiracy theorist. Almost always pushed by scientifically illiterate people, religious fundamentalists, the uneducated or misinformed, and - always - the paranoid.
"The government did 9/11! Jews control all of the banks as part of the Illuminati! NWO NWO NWO CHEMTRAILS!"
"You're a moron with this conspiracy theory nonsense. The 'Illuminati,' and 'NWO,' for that matter, have been conspiracy theories for well over a century. People were just as alarmist then as you nuts are now. And we're in some totalitarian unfree state now where you.. oh, have the freedom to express these nutjob hypotheses of yours?"
What can be verified. Not contained in the supernatural or holy books. The Amish do vaccinate and some do indeed have Autism; it is only a myth that they do not. The government isn't out to get you. Evolution's occurrence is an empirical fact, and there's far more than likely no god.
"What is the truth about vaccinations?"
"It's biologically impossible to get Autism from them."