Reading this thread, I think the question is really "What shouldn't you write a song about?" You have the "ability" to write a song about anything. My fifth grade teacher would be proud of me. For me, the question is neither of the above. It all depends on why you write a song. And who you are writing the song for. What do you want the song to do? Do you just want to shock people, or disgust them? To what purpose? Do you want to educate them? Do you want to activate them? Do you think that writing a song about child molesting will reduce the activity?

Finally, it comes down to how you write it. In the long run, that will determine whether the song has any chance of motivating people to work for change, or just disgusts them.

Jerry