Agreed. A woman I personally know was nearly the victim of a fake police officer about 15 years ago, back when she was in college.
As she was driving home on the interstate late one night, an unmarked car came up behind her and turned on a roof-mounted red, spinning light like you'd expect with an unmarked police car. She wisely called the police from her car phone to ask them to tell their unmarked car that she'd be continuing until she reached the nearest gas station, and they informed her that none of their units were pulling her over. They sent out an actual police cruiser to follow her and were able to apprehend the fake cop.
A couple of folks in these discussions are suggesting that cars should be smart enough to recognize police officers and follow their traffic instructions, which makes sense most of the time, but there are definitely cases where it does not make sense to follow the directions of someone who appears to be a police officer. The last thing we need is a rash of crimes where criminals dress up as police officers so as to confuse smart cars into pulling over unexpectedly.
All of which is to say, I'm okay with the default behavior being to follow "police" signals, but there should always be an override available to the driver in case they have good reason for not stopping, such as a belief that something fishy is going on or an emergency of sufficient severity to warrant disregarding police signals.