On the topic of open carry being a deterrent, I will elaborate on my thoughts. Since no two life and death situations are the exact same, a visible weapon may or may not be a deterrent to a devious act. Take this example, My girlfriend and I are walking to the grocery market around dusk. The road there is usually frequented by thugs and vandals. Naturally, I open carry on this trip to tell would be attackers that I am ready to strike if needed. A good analogy would be a coiled up snake, alert and ready to strike. This is a good deterrent to unarmed bullies who could attack and mug a helpless couple. Open carrying in this position is beneficial because carrying concealed, I wouldn't be conveying a message and could more likely become victimized.
On the other hand...
If I am in a store that is getting robbed and for some reason don't have my wits about me. I might become the victim of a preemptive strike. However, I usually scan peoples faces looking for potential threats. The eyes can tell alot. Just my two cents!