> what's so difficult about flashing a stock image to a device being serviced?

Yes, I think that would cover most cases if we take it to its logical conclusion of wiping all device state (hard disk). OTOH, a few points:

1. I would accept the need to wipe the hard disk if I had messed with firmware or the OS, but not if a couple of keys on the keyboard had stopped working. This implies that (for me at least) a meaningful distinction remains between these two "levels" of warranty service. Do you agree?

2. Activities like overclocking or overvolting a CPU have the potential to cause lasting damage that can't be reversed by re-flashing. Under the policy you're suggesting, it would be illegal for manufacturers to offer users the option "You can pull this pin low to overclock outside the supported range, but you will void the warranty by doing so", and too expensive for them to endlessly replace parts damaged by these activities for free under warranty, so that consumer option, rare as it already is, would go away completely.

3. I still think there may be some devices that are impractical to completely re-flash. According to this 2021 Porsche article [0], modern cars contain 70-100 ECUs (microcontrollers), each of which will have its own flash/EEPROM.

[0]: https://medium.com/next-level-german-engineering/porsche-fut...

> Yes. If I really _want_ to execute malware on my device, I should be allowed to do so by disabling the antivirus or disregarding a warning.

I agree.

> already the rule of law in "sane" jurisdictions, that manufacturer and mandated warranties are not touched by unrelated, reversable modifications to both hard- and software.

Do you have any examples of such jurisdictions? I think whether this is reasonable turns on how "reversible" is interpreted. If it means "reversible to factory settings", including wiping all built-in storage media, then it seems reasonable to me that manufacturers should support this (possibly modulo some extreme cases like cars that have dozens of CPUs). But I would not be happy with having my hard disk wiped if I sent in my laptop for repairs because a couple of keys stopped working, which tells me that (to me) there remain at least two classes of "problem that should be fixed for free under warranty by the manufacturer".