What does that even mean? What do you think "ethics" means? This is a nonsensical statement.
The consideration of what people in certain situations should or should not do, IS ethics.
Even if someone would say (for some reason) "but researchers should be able to do their work without consideration", that is making an ethical statement.
I understand why you would have a problem mapping this back to ethics, because if you'd formulate it as such, it would sound kind of bad: Researchers have no ethical responsibilities to the public.
You can't choose to not let decisions be guided by ethics, that's like claiming you choose to find your way without navigating. It makes no sense.
You seem like a living argument for ethical standards being imposed on your industry, by law if needed.
You're arguing that the force of law should prevent you from learning inconvenient things about the software you use.
You are harmed by them discovering a vulnerability and telling the world about it.
And if they discover a vulnerability and tell both you and the rest of the world, the harm may easily outweigh the benefit.
Suppose I go wandering around the city where you live, checking for unlocked house doors. I find that you've left your front door unlocked and gone on holiday. I then wander the streets shouting "Thomas's house is unlocked and no one's at home!". I also phone you up to let you know your house is unlocked.
It was your fault, not mine, that the house was unlocked and no one at home to deter burglars. In principle, anyone else could have come along and burgled your house, if they'd found it before I did. None the less, I think that in this scenario I have done you wrong.
The argument against your position that people are trying to get across to you is not that. It is that publication of vulnerability without giving heads-up and time to prepare solution to the vendor greatly increases the risk that a user will be harmed by attackers exploiting the public knowledge. Often substantial number of users are not going to mitigate or resolve the problem without their vendor giving out the official solution.
It's certainly reasonable to argue which kind of disclosure is the best way to achieve minimal harm, but my opinion is that it's unethical to disclose without considering what method of disclosure will do the least harm, or, worse, just not caring and going for the "biggest splash", as is what it seems these researchers did.
I would say they are all invasive evil maid threat vectors. Each one requires either physical access to the hardware or (as you stated) an already established root privileges. We all know that if you have physical access to hardware, it's essentially game over.
However. One of the vulnerabilities supposedly allowed to subvert UEFI secure boot. If that's true and allows to boot arbitrary media, then the others are equally feasible, because an attacker can boot into a root shell of their choosing.
The timing in this disclosure reeks of malice, though. Giving a 24h advance warning basically allows the outfits to claim that they disclosed vulnerabilities to manufacturer before going public. Technically true. Just highly misleading and dishonest.
I have personally no beef with full disclosure, and have advocated it as a viable mechanism since the mid 1990's. I also happen to think that responsible disclosure is a good approach, but it definitely needs the threat of FD as a stick, because otherwise vendors would not have any real incentives to work on addressing security bugs. Name-and-shame does work.
Let's get back to AMD flaws. Giving a really short window? Basically just enough to have an initial PR response ready? Have the decency to go full disclosure. Or give a full month. AMD won't be fixing the bugs before news breaks in either case. Just don't claim this is anything but a maliciously crafted exercise with ulterior motives.