Our right to free speech is not granted by anyone's consent or by government decree. It preexists the state and cannot be taken away.
We hold this truth to be self-evident. We are endowed by our creator with certain unalienable rights.
If any government becomes destructive of these ends, it is the right of the people to alter or to abolish it.
You can wax poetically all you want about endowment by the creator, but try saying racial slurs on daytime TV and see how long that lasts.
Advertisement is just another form of speech that can be limited.
You're conflating two senses of "free speech". Free speech is an ideal, which our society does not fully reach (as you correctly pointed out). But in the US, "free speech" is also sometimes used to refer to the legal protection from the first amendment. And in your example, that does apply. I can say all the racial slurs I want on TV, and it would be quite illegal to put me in jail for it.
This is not true.
Under 18 U.S.C. Section 1464, “[w]hoever utters any obscene, indecent, or profane language by means of radio communication shall be fined under this title or imprisoned not more than two years, or both.” Under 18 U.S.C. Section 1468(a), “[w]hoever knowingly utters any obscene language or distributes any obscene matter by means of cable television or subscription services on television, shall be punished by imprisonment for not more than 2 years or by a fine in accordance with this title, or both.” Likewise, under 47 U.S.C. Section 559, “[w]hoever transmits over any cable system any matter which is obscene or otherwise unprotected by the Constitution of the United States shall be fined under Title 18 or imprisoned not more than 2 years, or both.”