How did the Left gain the upper hand with same sex marriage? A technique identified by Cass Sunstein and Timur Kuran explains the simple, effective process: Availability Cascades.
An AVAILABILITY CASCADE is a self-reinforcing process of collective belief formation by which an expressed perception triggers a chain reaction that give the perception increasing plausibility through its rising availability in public discourse. The driving mechanism involves a combination of informational and reputational motives: Individuals endorse the perception partly by learning from the apparent beliefs of others and partly by distorting their public responses in the interest of maintaining social acceptance. Availability entrepreneurs -- activists who manipulate the content of public discourse -- strive to trigger availability cascades likely to advance their agendas ("Availability Cascades and Risk Regulation," Timur Kuran and Cass Sunstein, Stanford Law Review, 1999).