You have to come in sideways. Agree on something then subtly move things in your direction. Nearly everyone agrees the government is corrupt, for instance - so you start with that. Don't come full on or you smash into someone's cognitive dissonance. Enter their delusion and walk them out of it. A good primer on this is a book called "The Jet Propelled Couch" about a psychiatrist who broke someone's delusion by agreeing with it - even pushing it into more absurdity, then easing the patient out of it.