I believe cases like this hinge on the notion of informed consent (they were not informed the product is defective) and reasonable expectations (it's reasonable to expect that by now, after so many years, Microsoft would have learned how to make an operating system that does not destroy user data).

No they don't. Failure to read the entire agreement is not a defense. It's binding if you did some affirmative act (including using the product) after notice of the terms, even if it's only a link. Reasonable expectations mean nothing in this context. Will likely be sent to arbitration on an individual basis.

If using every product requires reading a dozen pages (at the very least), then how do you expect to use literally any mobile phone you can buy in a store?

I could pretty easily counter with: it's reasonable to expect people to backup any files that are important enough to them they'd sue over it.

At the rate cheap spinning laptop hard drives fail, you are literally an idiot if you aren't backing up important files. It's not IF they will fail, it's when.

Yeah, that's why I used consent. Consent is a messy topic that requires a best effort and careful deliberation. I definitely agree that EULAs like that are in a dangerous gray area.

Ah, that's the issue. "You have left your computer unattended; that's consent enough for us to install WinX. Too bad, sucker, you should have purged GWX and aggressively prevented it from coming back; anything less, and we consider it as consent."

There have been incidents of rogue upgrades to WinX despite a lack of consent; in such cases, your argument is moot.

That's really not the reasoning. The real reasoning is: "You consented to allow us to automatically install software updates on your computer. Windows 10 is a software update, se we installed it automatically."

Basically, people want to trust Microsoft to install updates it thinks are good and necessary, and then they get mad when they disagree with MS about what's good and necessary.

Well then. "We have changed your system so that your business-essential peripherals are no longer working (because vendor does not have drivers for Win10 just yet)" is good, yes? I sort of prefer to make such decisions in a non-automated and in-house way, so that the business case for upgrade can be considered on its merits. Instead there's unplanned downtime, because someone in a completely different company had to fill their quota of Win10 upgrades. Good and necessary for that person to get their KPI bonus, customers be damned.

(Also, your attempt at doublethink fails because of GWX: how many other updates had a special pop-up notification "please give us consent to specifically do this"? Oh wait, zero, throughout the existence of WU.)

Windows 10 upgrade, no matter how Microsoft words it as an update, is actually a whole system replacement. So while most users trust Microsoft for keeping their system up-to-date, I don't think they approve its deletion and replacement by something else.

Then they misplaced their trust and should have picked a vendor they agree with more, because MS does think of it as an update. What "most users" think is irrelevant in court.