I bet there are many who think of poetry readings as music of sorts. While I can see it as such, I am not one of them. That said, I suppose an a capella rap would not be a "song" to me unless it's sung.
Plain speech? No, not me. But I'm sure there are those who hear "music" in everything. I think I would like to be one of those people.
That is my point about rap. They are just speaking a poem over background music. They are not singing.
People sing a song. Nobody speaks a song.
Song or not:
When a man lies, he murders some part of the world.