Killing Rap and Artistic License in Criminal Court

In the New York Times article, “Acquitted of Murder, Rapper Is Convicted on Weapon Charge” Lorne Manly discussed the recent new assault on the First Amendment. Currently, prosecutors are trying to introduce rap lyrics as confession evidence in pending criminal trials. Their argument is that merely setting the confession to music or in the form of a rap does not detract from its incriminating nature. Furthermore, courts are admitting this evidence.
What ever happened to artistic license? When Johnny Cash created his alter ego, an inmate in Folsom prison who had “shot a man in Reno just to watch him die,” No police officers began to comb their cold case files for an unsolved homicide in Reno. People understood the concept of artistic license.
This development could be the beginning of the end for rap. What do rap artists rap about? Not sunshine and rainbows but life observed: drugs, guns, gangs, shootings, police harassment etc. Consequently, if police and prosecutors can use the lyrics to criminally prosecute, the chilling effect on the desire to write and perform a song or rap is enormous. Why risk the harassment, possible incarceration and legal proceedings in order to express oneself? If that is not a violation of free speech, what is?