Deterrance is still a valid reason for carrying a weapon. Intimidation will always be a factor to the common crook. If you look tougher than you're worth, the common crook will not try to rob you.
Those that are not deterred are not the common crooks. They are either desperate, uncommonly stupid, or legitimately don't care. Against this type of criminal, readying or firing your weapon is an escalation that is almost universally not in your best interests. Your life is worth more than your wallet, every single time. Your life is worth more than your car keys, every single time. Deliberately pulling a weapon on an armed robber isn't self-defense, it's idiocy.
Against those kind of criminal that will shoot without the escalation, the weapon exists as a last resort. This kind of criminal will not tell you to stick 'em up in the cliche sense. This robber will start shooting anyway. This is the only scenario in which returning fire can reasonably be a proportionate response. Furthermore, if you find yourself in this situation, you are probably doing it wrong. This kind of criminal does not walk along a crowded mid-day street looking for a mark. This kind of criminal preys on those isolated from help and in a secluded place when no one is around. Common sense, avoid those places.
Concealed carry offers none of the advantages of deterrance. Concealed carry deters no one. Concealed carry offers no advantages over open carry other than that you can surprise your opponent with return fire. If you are returning fire, you have either handled the situation incorrectly, or the situation was headed there anyway and the concealed part offers exactly zero benefit over open carry.
Don't put words in my mouth. I very explicitly support open carry. I very explicitly do not support concealed carry, because the benefits gained are minimal and the risks taken are disproportionate.