Thank you for educating us! Some local people really make their own country look really bad to the tourists. Sometimes, I prefer to use the public transportation to get to airports, avoid taking taxi as much as I could....
It's good that you stood up for yourself against the driver and fortunately, the outcome was good but it's risky in a foreign country where you don't speak the language. He could have taken you to some dodgy neighborhood where his "friends" may be waiting for you or left you in a remote part of Istanbul. Getting ripped off by taxi drivers is part of the cost of traveling in a foregin country.