Through millions of Americans voicing their opposition to the movie and Moore's attempt to profit (and those theaters that show it) from a movie that undermines the War on Terrorism.
Again, I don't have the power to suppress a movie. But Americans have the power of their voices to express themselves. If they DO then movie theaters will choose not to show it.
That's the distinction. You have to respect the right of free speech of those who disagree with Moore.