The area surrounding USC med is not as crime-ridden as that surrounding the undergrad campus. It's more of a low-income immigrant community. Since USC med is a commuter school, the surrounding area hardly affects the student body. You drive to school and then you drive home (to nice suburbs like Pasadena, South Pasadena, etc).
Another reason why someone would get a bad impression of USC on interview day is if he didn't like the County atmosphere in the first place. The patients are poor, County's facilities are poor, and the ancilliary staff are poor. If you want a nice, clean environment with nurses who smile, County ain't it.
We do have our fair share of students who whine about everything, so if you ran into them, that would also give you a negative impression of USC.
As for the positives of SoCal: weather, beaches, best ethnic food, 4 hours to Vegas, and 5.5 hours to Mammoth. The latter two are important because you'll want to take mini trips over the weekend during school.