"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the government for a redress of grievances." What is the statutory reason that they are not allowed to do this? Sincere question.
"The Supreme Court has noted that the FCC has an expansive mandate to ensure broadcasters operate in the public interest." (National Broadcasting Co. v. U.S., 319 U.S. 190, 219 (1943).) It's like shouting fire in a theater when there is none - that would not be in the public interest. Neither is broadcasting lies to deceive the public.
Imagine I pay a news station to run a story about a hospital (for example) which I believe to have saved many lives and I expect will continue to do so. Arguably my advertisement is in the public interest, because it brings attention to a potential health benefit.
What then, hypothetically? Is "public interest" still a justification for the fine?