Are you saying that the employers of all murderers, rapists, etc are responsible for looking into the future and determining whether or not an employee will do something illegal?
not in the least, but providing a service that allows people to connect but provides no promise of a backgroudn check and simply facilitates offline contact (i.e., craigslist) seems notably different from Uber's directly connecting of customer and driver, facilitation of interaction, promise of background checks, and charging of a customer safety fee.