Question for everyone, ESPECIALLY police officers?

Your reasoning is completely correct. If the suspect was not reaching for a weapon, I would guess that he was hiding something he didn't want the officer to find. The officer was trained to use his best judgment in cases just like this and was correct in his response. It is sad that someone died, but it was the result of the passenger's actions. Any time an officer discharges a firearm, they are put on administrative leave until the investigation is complete. It is not necessarily a sign of guilt or wrong doing on the officer's part.