If a car service manual said "replace the engine" (along with detailed instructions on how to do so) when a spark plug went bad, would you consider that acceptable just because the manual were released?

There are many service manuals for cars that recommend procedures that independent auto shops and shade-tree mechanics do not follow.

Get a short in a wiring harness? The service manual for your car will almost certainly recommend replacing the entire harness which is a very labor intensive and expensive procedure. Will mechanics do this? Depends on which shop you're at and who is paying.

If there are multiple ways to solve a problem, an official service manual will typically list the safest and most repeatable solution. Rarely do they list any alternatives to this.

Well, part of me wishes this particular "car" wasn't separated into two replaceable pieces. A fender-bender or bad battery shouldn't warrant replacing half of my car! Not only is it ridiculously expensive, but it's insanely wasteful if the half it's replacing isn't being salvaged for components.

Apple has the resources to fix this. They choose to actively neglect it, since they have a very successful side-business dedicated to replacing your iDevices at-cost.

That's a fair criticism of the design of the device, but I fail to understand iFixit's argument that this is the repair program's fault.

A more apt analogy is the spark plug is stuck, stripped or broken.

In that case should they provided detailed instructions on removal where that risks destroying the engine or at least the heads?

I'd definitely risk destroying an engine if the alternative were throwing it away and replacing it while there was still a chance it was fixable. Who wouldn't?

My point is the company is not going to provide you instructions that would likely damage or destroy the product, not debate whether or not one should attempt those procedures.

If I was following the shop manual and I broke a head bolt off in my engine block I would take it to a machine shop, but I wouldn’t expect the auto maker to provide instructions to remove a broken head bolt.

Businesses often wouldn’t. They have additional costs that you don’t have when you’re repairing your own stuff. Labor, liability, capacity, brand image, etc.

Automakers have been known to replace entire engines for recalls involving only one part of the engine, when they have concerns about one of the above factors.