It's hard to know, but I'm guessing that the possibility of being shot and killed by a police officer does very little to deter crime. Sometimes the perp thinks about a crime ahead of time and effectively weighs gains against risks, and in that case they are thinking of being caught and possibly sentenced, not about the arrest itself. Other times the crime is spontaneous or out of complete desperation and again the perp is not thinking about the danger of arrest or anything else for that matter.
Only when confronted by an officer does fear of that officer come into play. And in those cases it's really hard to say whether extreme fear of the officer does more good than harm. If one feels like one's life is in danger, it's all about fight or flight.
In general I think we focus too much on deterrence when it comes to our justice system. Consider these goals of the justice system: reformation, protection, deterrence, and revenge. Non-lethal tech is focused on the first two, and lethal tech is focused on the last three. In general we do a really bad job at reformation, so it makes sense to focus more effort there.