Surely the point is that many songwriters want to be thought provoking (hence Sting writing about suicide or a pretty love song that is actually about stalking), or even provocative (most songs written by Jagger).
As mentioned by others above, Jagger goes for a clean sweep with Brown Sugar - slavery, rape, his love (lust) for a black girl and interracial relationships (a controversial topic in America in 1971), all with a subtext of heroin use! He did say that he would have self-censored if he was writing that song today, but those were hardier times!