Q: Someone I know uses the turn signal to signal if a car in front of us is turning. I say we shouldn’t because the vehicle behind us will then expect us to turn. We should only signal what we are doing in our vehicle, correct?

That sounds very strange to me! You’re right, brake lights should do the trick and a signal when you aren’t turning could easily get you into trouble… What happens after the car in front turns, you then suddenly turn off your turn signal and continue straight ahead? when oncoming traffic thinks you’re turning and so do the cars behind and all around you? This sounds pretty dangerous if you ask me. Just my opinion..

Also it should be common knowledge that when driving in a left lane, sooner or later you may have to wait for someone to turn left, this is a fact of life! Just like if you’re driving in the right lane, you may have to stop because the car in front of you is turning right and stopped for a pedestrian. Drivers should be used to these everyday occurrences… shouldn’t they?

Reference: 

SAE International: (not exactly the same issue, but definitely related)

“The data presented here should serve as a wake-up call to all citizens, vehicle manufacturers, research institutes and government entities that are involved in vehicle safety. A greater focus is needed at the highest levels to create an overall awareness that turn signal neglect is an injury and death problem, as well as a property damage problem, and that the in-vehicle technology to combat this is available and adds no cost. Turn signal neglect is a problem that causes more crashes than distracted driving and if “neglect” of the use of turn signals is the message in this study, then “neglect of the neglect” is the story of the automotive safety community.”