Think what would happen if you were to walk up to a guy in the street and say onto him "You, sir, are a fucking asshole." Would you, realistically expect him to just acknowledge your right to call him such and go about his merry way down the same street?
Actually, pretty much, yeah. I might expect to get flipped off as he continues on his merry way, but that's equally protected speech.
What do you expect? That he tries to hit me? Because battery doesn't get constitutional protection.
Bonus points if you say this to a police officer of a major city, or uniformed military personnel.
I have further expectations from police officers and uniformed military personnel. Not only do they have to ignore my calling them fucking assholes, they don't get to flip me off in return. Because it would be unprofessional behavior. That might not be what actually happens, but they should be punished when they react in any other way.
In accordance to the First Amendment, the Gov't made no attempt to censor the song or prevent him for making it public by his chosen means. Be ready for the consequences after doing so.
There are consequences to speech. His friends may shun him, the media may react to the lyrics and condemn him. The government cannot take any action for pure speech. Other than possible investigation of a threat, but I wouldn't consider lyrics to a song to be a threat anymore than I consider the vast number of times the white house was attacked in a movie to be a case of the writer and director of said movie threatening the white house.