They're not worthy of happiness or acceptance if they don't believe you. Back this up with fear. Unless they absolve themselves by believing you, something bad will happen. Justify their anger toward things they don't understand, and promise them love if they believe your lie. As time goes on, and more people believe your lie, a community will form of people who believe it.
Communities give people a sense of belonging.
Communities appeal to people's fundamental need to socialize. Appeal to people's pride by telling them they're elite if they belong to the community, but worthless otherwise. People have to be motivated to spread it. They will be motivated because they want to make their community larger initially. They'll want to tell other people because the sense of community and love from others bound by a common thread will make them happy.