(genuine question)
EDIT: I think the point is that I feel like I have the choice to escalate and take action in a way that eliminates the threat if I see that it is required.
I don’t have any problem at all with people resorting to lethal force as a means of self defense, and if this was violent crime we were talking about, I’d probably see it differently. As far as shoplifting, I do believe that a community of armed, on-edge people looking for criminals is likely to be more of a threat to public safety than the criminals themselves. I think more effective surveillance and forceful prosecution—as well as whatever social measures can proactively reduce crime—is a better approach here.
I mean, maybe you could block a thief’s exit while producing a handgun, and create a standoff until the cops arrived. That still sounds pretty reckless for something like shoplifting; getting into an altercation that results in firing a gun in a store is a risk to everyone in the vicinity. I remember when some woman shot out the tires of somebody trying to steal a ton of stuff from Home Depot—she was arrested. Both the cops and other gun owners thought that was incredibly irresponsible.
I doubt a thief would stick around for the cops to arrive. And I do think everyone knows you don't pull a gun until you're ready to fire it to neutralize a threat. (A truck is probably not a theat unless it's trying to run you over.)
Retail theft—someone grabbing stuff and fleeing the store—is a different deal. If you blocked the person from leaving and they threatened you, again, you might be able to justify drawing a weapon. But threatening deadly force against someone who’s running away isn’t the same situation.
As you said, you don’t draw a gun unless you’re willing to use it. If I were a store customer or employee, I’d be more worried about armed hero-types overreacting and possibly killing me, rather than someone stealing stuff and trying to escape.