I see slowing down, well at least taking your foot off the gas, approaching a red light as part of defensive driving. No one needs to race to a red light, so they can slam on their brakes feet from the light, only to gun it cause the light turned green just as they stopped.
It's bad wear and tear on your car, especially brakes and tires and totally trashes your gas milage. So, no I don't think anyone is rude to slow down approaching a red light or a green light that you know is short and will be red when you get there.
Just for some perspective, my car is over ten years ago. I've only had to replace the brakes and tires twice ever and one of each of those was for defective product...I had a tire blow and my front brake pad broke in half.
I think your friend should pick up a defensive driving manual or maybe take one of the classes. Really, I think a lot of people should...teaches people to be more aware of their surroundings, how to avoid hazards and accidents and Patience.
Waiting to turn left is just part of the life of a driver.