RE: This will teach you to street race
Lear, I think it was for both racing and the stolen parts. So in your example with the stop light racing, you would probably just get a nice hefty fine, and depending on the mood of the officer, could get impounded and then you would have pay for that to get it out.
Also there could be a third reason as well. I don't recall them saying it, but with those parts they are putting on, could be that the car is not street legal.