To reduce negative outcomes, we use risk management: assessing the likely lifetime cost of the flaw, and taking cost-effective measures to reduce the risk to an acceptable level. As a familiar example, redundant mass storage drives are much more cost-effective than high-reliability mass storage drives.
And the DC-10 was not decommissioned. It is, in fact, still in service.
https://www.flightglobal.com/safety/us-faa-broadens-md-11-gr...
FedEx did and they retired them in the last 5 years because they had reached the end of their economical service lifetime and not because of any major flaw.
Aviation rules are written by blood, you either follow them or you add a few more lines with your own blood.
Please, what fool subjects their own blood to the absence of regulation? If you've got blood on your hands, much better for it to be a customer that has already paid you.
The fundamental reality is, we can always spend more to prevent another death; and we must draw the line somewhere.
People don't like it, but your latter example is the risk management I'm talking about, and it's unavoidable. Nobody can make airplanes that have no risk of killing people - the only answer would be no airplanes at all (which would result in more automobile deaths, more deaths because life-saving resources are unavailable, etc.). The calculation of cost per death prevented is a real one, and is done by manufacturers of planes, cars, etc.
The problem with your wording is the criteria of paying damages, rather than the industry-standard value for human life. Again, that is awful to think about but there's no way around it.
Edit: And I'm not saying, at all, that Boeing made the right decision here. I don't know enough to say, and Boeing's safety reputation is poor.
And "shit happens; suck it up, buttercup" is not an approved PHA determination.