Who should be second in line for liability (when the actual culprit isn’t caught or can’t pay) is a more debatable question, I think, but I still do not see any clear reason for a default of assigning it to the product manufacturer.
Your principle 3 says we should assign liability to whoever can most cheaply prevent the problem. My model says that will sometimes be the manufacturer, but will more often be the victim, because they’re much closer to the actual harm. For instance, it’s cheaper to put your valuable heirloom into a vault than it is to manufacture a backpack that is incapable of transporting stolen heirlooms. Also consider what happens if more than one product was involved; perhaps the thief also wore shoes!
My model also predicts that in many cases both the manufacturer and the victim will have economically-worthwhile mitigations that we’d ideally like them to perform. I think the standard accepted way of handling situations like that is to attempt to create a list of mitigations that we believe are reasonable for the manufacturer to perform, then presume the manufacturer is blameless if they did those, but give them liability if they failed to do one that appears relevant. Yes, this is pretty much what you complained about in your malpractice example. Our “list of reasonable mitigations” will probably not actually be economically optimal, which adds inefficiency, but plausibly less inefficiency than if we applied strict liability to any single party (and thereby removed all incentive for the other parties to perform mitigations).
Who should be second in line for liability (when the actual culprit isn’t caught or can’t pay) is a more debatable question, I think, but I still do not see any clear reason for a default of assigning it to the product manufacturer.
Your principle 3 says we should assign liability to whoever can most cheaply prevent the problem. My model says that will sometimes be the manufacturer, but will more often be the victim, because they’re much closer to the actual harm. For instance, it’s cheaper to put your valuable heirloom into a vault than it is to manufacture a backpack that is incapable of transporting stolen heirlooms. Also consider what happens if more than one product was involved; perhaps the thief also wore shoes!
My model also predicts that in many cases both the manufacturer and the victim will have economically-worthwhile mitigations that we’d ideally like them to perform. I think the standard accepted way of handling situations like that is to attempt to create a list of mitigations that we believe are reasonable for the manufacturer to perform, then presume the manufacturer is blameless if they did those, but give them liability if they failed to do one that appears relevant. Yes, this is pretty much what you complained about in your malpractice example. Our “list of reasonable mitigations” will probably not actually be economically optimal, which adds inefficiency, but plausibly less inefficiency than if we applied strict liability to any single party (and thereby removed all incentive for the other parties to perform mitigations).