True, but as integrator, Boeing is still responsible for ensuring the quality of the final product.
If I was running a US taxi service and bought a fleet of flawed Indian cars that caused crashes, I think I would be partially responsible.
I assume airlines do some degree of due diligence and, I believe they choose the engine type if there are options available but you probably overestimate the ability of a business whose primary job is to ferry passengers from point A to point B to do a serious design verification of every tiny detail of an aircraft. And those details can be tiny; take the case of the Airbus engine disassembly mentioned elsewhere on this thread.
Car manufacturing is a regulated industry. When I buy a car in the USA, even for my taxi business, I shouldn't need to hire a team of engineers to verify that it was properly designed and won't spontaneously combust. I should be able to assume that if the car is being legally sold to the public in the USA, the manufacturer has demonstrated that it meets some basic safety requirements set out by the government. I obviously have some _operational_ responsibilities (e.g. taking my taxis out of service if they're recalled for a design flaw), but I wouldn't consider myself responsible at all if my taxi happened to be the first 2025 Toyota Camry that spontaneously combusted from some design flaw.
Regulators aren't perfect but this is one reason they exist. The FAA has a set of requirements for manufacturing and selling planes in the USA and they have a set of requirements for operating an airline. If I'm operating an airline and the FAA tells me that the verification of an airplane's design and its assembly is the manufacturer's responsibility and not mine, I don't think it's fair to hold me responsible if my brand new airplane falls from the sky because of a design flaw.
Not that it is relevant to the overall relevance to the aviation argument here, but just in regards to cars in the US -- you often would be held liable for that, depending on which specific liability we are talking about, what the damages are, and in which jurisdiction you are operating in.
- It's the assembler's responsibility to make sure the exit door bolts are properly tightened, and
- It's the manufacturer's responsibility to find assemblers that correctly tighten door bolts, and the manufacturer's responsibility to design doors that don't explode, and
- It's the airline's responsibility to find manufacturers that design planes with not exploding doors, which are assembled by assemblers that correctly tighten door bolts, and checked by the airline's own maintenance teams during regular servicing of the planes.
Everyone should be looking over and double-checking everyone else's work. But that's not how the 737 MAX was designed or built.