Rap, originated from poetry.
Black people wanted to apply the rythms from Africa into their newfound faith of Christianity. Their hymns and songs began to reflect it, freedoms songs, same deal. Eventually, rap moved away from purely religious explorations and slowly into the mainstream.
Rap music does have a meter to it, though, unlike poetry, it often changes. That is simply due to the fact that music is filled with a change in 'pace.' The lyrics need to fit that, so the music and words need to flow together.
Yes, yes, you will encounter crap rap - i.e. mainstream junk. But dig a little deeper into people like J5, Talib Kweli, and the Spooks and you'll find some good poetry.
Perhaps your parents don't think it is b/c they never encountered poetry, its not in the form they were taught. But thats rediculous seeing as poetry is a reflection of emotion and emotion changes from culture to culture and emotion to emotion, poetry will come in all types of forms.
East Coast - 'Bitch Please, Ride with Steeze'
COC - Session C