It's a bad influence. Think of the children!
This argument actually predates hip-hop by a whole lot. People said the exact same thing when jazz blew up, when R&B blew up, when rock-n-roll blew up. All these years later, those once-endangered kids have grown up just fine—and now they're levying the exact same arguments against their own kids and their crazy hip-hop music. This is the way of the world. Forever has been, forever will be.
But today's kids are more than all right: As mentioned earlier, crime continues to trend downward, inversely proportional to the popularity of rap, and the generation weaned on hip-hop can be said to be, at least by certain measurements, less racist (hi, Obama) and less homophobic (bye, DOMA) than their forebears. This despite (or maybe even because of?) all that devilish rap music being pumped into their ears.
For the sake of brevity, we won't list all the hip-hop songs filled with positive messages for the youth, from Nas telling black children to be proud of their heritage in "I Can" to Slick Rick imploring kids to "get ahead and accomplish things" in "Hey Young World." We'll just let the late, great O.D.B. tell it: "Wu-Tang is for the children."