Given specific areas, the person, their movement, their actions, I would say that 90% of the shootings are justified. Better to be judged by 12 than carried by 6. When you look at the reports, the media loves to spin the story around to make you believe the "unarmed suspect" was 100% innocent.
Granted I saw your comment on the 30 rounds into a suspect aswell. Given most situations, adrenaline is running so high with most law enforcement officers is the reason why their triggers were pulled that many times.