There really isn't much to elaborate on, for something to be called music it needs to sound functionally different with and without musical instruments. Rap sounds basically the same either way. That is not to disparage those who like it, people like what they like however it does not fall under the true definition of music. It would be more akin to a kind of poetry. Btw, I used to listen to rap but have grown out of it. The above was told to me by a fifth grade teacher I believe (she is probably long dead) at the time I believe I wanted her to be full of shit but could not really refute her argument.