You can say anything you want, as long as you do not infringe on my rights, such as by consuming my resources (time, telecom services, fax paper, etc) when I explicitly said not to (via a Do Not Call listing, etc.)

It's similar to a No Trespassing sign; you can picket on public property (free speech), but doing that on private property (when marked with a sign that fit certain criteria, in most states) might get you arrested and charged with a crime.

In the U.S., the rights of the individual generally trump "public interest".