Need a real-world example? In a UK murder trial, prosecutors used a defendant's drill rap lyrics as evidence, and courts have repeatedly said those bars read like confessions, not art. If song lyrics can put someone in prison, they can definitely shape how kids treat each other.
As for your violence stats dropping since the 90s, sure, playgrounds got safer while rap got darker. That doesn't mean lyrics are harmless; it means we've built better fences. Meanwhile, disrespect is the quiet violence that doesn't show up in crime statistics. It's the kid who calls girls trash because his favorite rapper does. That's not correlation. That's rehearsal.