Free speech
Most people will not support free speech on principle. They will support it when it helps them and fight it when it harms them. People vehemently oppose free speech when it helps in spreading of bad ideas. Ideas make up people’s world views. People have different world views because they think differently. There is no objectively good or bad world view. So there are no good or bad ideas. But an idea seems bad to people when it threatens their world view. People’s world views are under constant threat from new ideas. Free speech is the battleground in which ideas compete. But people value their world views and will go to great lengths to protect it. They can protect it as long as they have free speech as it gives them access to the battleground of ideas. But if their speech is censored their world view is effectively killed. Left with no other option they will resort to violence to save their world view. Conflict from such violence can lead to catastrophic war as people can value their world views more than their own lives. Protection of free speech is a defence against such conflicts.