Human drivers also pull over when people who look like the police ask them to.

Sure, if you're willing to risk going to jail for impersonating a law enforcement officer.

Fair enough. I'm sure some would be willing to do that, but likely not many. I do think it is going to be very interesting to work out some of the scenarios if we do get to Johnny Cab style self driving cars.

If you're willing to risk jail, disrupting traffic is ridiculously easy, self-driving cars or not.

Is fooling a computer system into thinking you are a police officer the same thing as fooling a person?

People are. See South Africa, Brazil, etc.