But the First Amendment protects against the Government; it does not leave us at the mercy of noblesse oblige. We would not uphold an unconstitutional statute merely because the Government promised to use it responsibly. [...] The Government's assurance that it will apply [a statutory provision] more restrictively than its language provides is pertinent only as an implicit acknowledgment of the potential constitutional problems with a more natural reading.

United States v. Stevens, 559 U.S. ___, 130 S.Ct. 1577 (2010) (Opinion of the Court).