The fact that they are willing to use this switch in this way is far more damning than if they had done nothing at all. The problem is that one of the so called 'allies' here is behaving in ways that make it very difficult to sustain using that term.
And military alliance or not, there is such a thing as justified defense and it used to be in the decades leading up to 2015 or so that the USA was a reliable defense partner. I realize that 10 years is a long time, but a lot of people have been very slow to realize how far the rot has worked its way in.
Weapons bought and paid for by EU money are being withheld, and that's in light of daily slaughter of Ukrainian civilians (I have no other word for what is happening there).
I agree with you this is the de facto situation, but they thought they were in an alliance because of the Budapest Memorandum.
2. No point of the Budapest Memorandum implied that the signatories had to defend Ukraine.
Paragraph 4 essentially states that signatories have seek UN Security Council action if Ukraine became the victim of aggression or a threat of aggression involving nuclear weapons.
Ukraine isn't victim of aggression involving nuclear weapons, and even if it was, the signatories merely said they would escalate the matter to UN's security council.
Another paragraph had signatories (China, France, US, Russia, UK) to refrain from using force against Ukraine. Russia has violated this point.
All this lawyering-after-the-fact ignores that if what you say is true then Ukraine got screwed over, both by Russia and by the other signatories of that 'note'.
So, the normal response of other parties to such an agreement would be to ensure that all signatories stick to the agreement. Since the only party that conceivably could break it was Russia I'm pretty sure that that was taken into account when the agreement was signed, anything else would be stupendously naive.
The end result of this is that non-proliferation is dead, and that is a net negative for the whole world.
Ukraine had no alternative.
We have various analyses in the National Security Archives, reports and memoirs from US diplomats involved in the matter: the US was the primary actor that pressured Ukraine in giving up their nuclear stock pile.
Ukraine could not operate it (everything from security, cryptography, controls, navigations, etc was in Moscow anyway), could not maintain it, and could not even guard their stock pile.
The biggest risk for the United States was that with the rampant corruption and sell off of soviet weaponry on the black market there were the wrong incentives for too many actors that could bring soviet nuclear weapons in the hands of bad actors.
You cannot outsource technology that is critical to your defense.
You either develop it on your own or you operate it along your allies.
Ukraine is in no military alliance, so Musk or not, it is consistently liable to the unreliability and whims of external providers, either public or private.
Which is why I'm very negative every time I hear European countries are renting from Space X instead of investing in common space technology. The day that somebody in Washington, or Dallas, decides to turn the switch off, you're off.