I didn't read your link (I probably will later; it looks interesting

), but for me it all seemed to go downhill when gangsta rap became
popular.
I've seen critics (or "critics"

) blame rap groups like N.W.A. and people like Ice-T as perpetrators of a violent culture, and they're right to a degree. But the way I see it is those rappers were
products of a violent and impoverished environment. Many urban areas were extremely hostile and unhealthy, especially after the crack epidemic in the late 80s, so I don't necessarily think it's fair to attribute all the blame to just the rappers.
Gangsta rap was never meant for mainstream society. It was a subgenre directed at a very specific target audience (typically black kids growing up in rough areas who could relate on a very tangible level to the struggles in many of those lyrics). Record labels caught onto the popularity of gangsta rap from the high sales in urban areas and basically exploited it for profit.