All you have to do is plant the seed of doubt in their minds. They will struggle with it, and reject it and get angry just as people did when Galileo told them the Earth revolved around the Sun. But eventually an idea sinks in, people start considering the possibility themselves and thinking about whether it MIGHT be true. You have to start somewhere. I have seen people change over the past couple of years from being totally supportive of conventional positions to now believing that many "conspiracy" theories are actually true...including the idea of death squads in this country. They come to the idea themselves once they realize that they are being lied to constantly and that the media/govt stories simply don't make sense.

They just have to get over the shock of the truth.