If you ask ten different cartographers to create a map of the world, you'll get ten different maps. That hardly proves that the world doesn't exist.
We decide where the line should be drawn through argument and public debate, and by refusing to comply with weaker definitions from anyone who can't convince us using reason that where they want to draw the line is actually in the interest of the people.
The US draws the line at true threats, and inciting imminent lawless action, among others.
New Zealand now draws the line at simply sharing a manifesto along with anything else decreed by the Chief Censor.
China is much more strict, but who's to say where the line should be drawn? Not even western governments agree.