Left turns lead to gridlock and delays.
I work on one side of the capital building, and my child goes to school on the other side--exactly one mile away. There are days that the one mile drive has taken 45 minutes, because of delays caused by a left turn. When drivers stop in the intersection before a light changes, that prevents people from turning left. Pedestrians who are crossing at the same time as the people turning left also slow traffic. Sometimes the garage that I park in gets backed up by several floors because of the delays on the street level, a couple of blocks away.