NATO directly fighting in Ukraine is a massive red line and a huge escalation that pretty much nobody wants.
(Russia already published it's keen to keep going. You can discuss whether that's just posturing or not, but that part's public)
When someone argues it would be a huge escalation for the US, UK and France to directly defend Ukrainian territory against Russia's attacks, they should explain how the same nations directly defending Israeli territory from Iran's attacks is constructively and strategically different.
The other would almost certainly end up being called WW3, and would likely involve at least a limited nuclear exchange.
The reason it was “de-escalatory”: It helped Iran prove what it sought to prove: no AD in the world will stop their missiles from getting through. For Israel it provided the face-saving “99.9%”.
Also, the Ukraine situation has no Jordan, Iraq, accessible ocean (ask the Turks about that) to operate from.
https://vatniksoup.com/en/nuclear-threats/
Don't let the ridiculous, empty threats of Russia warp your perceptions of what's possible.
This is what Russia would like you to believe (and to repeat on their behalf). Much of Russian propaganda is aimed at instilling fear in target populations. The goal is to demoralize their adversaries' civilians in order to undermine support, hence political and military will for opposing them.
Russia has been dictating the terms and rattling the saber with nuclear threats, etc. from the start. Initially, Putin wanted people to believe he was so irrational that he'd use nukes at any provocation. But, the fact that he threatened instead of simply using them was the clearest sign that he's rational and doesn't want this war to escalate. The worst possible thing for Russia is for the West to fully commit.
In short, if using nukes was advantageous to Russia, they'd have already used them. On the conventional front, they need to feel some actual risk. Otherwise, they commit to an ongoing war of attrition where theirs is the bigger population/force and it's Ukrainian cities that are being leveled. Time is on Russia's side.
So, it's already a war. The West either wins it or loses it, and you don't win on your enemy's terms. Aiming for a stalemate and "negotiated peace" (which Russia won't honor in any case) is extraordinarily costly, especially when the war is being fought exclusively on your (or your ally's) territory. i.e., it's a loss.
The West needs to realize it's in a war and go on the offensive, politically and militarily. Redeploy Russia's frozen assets to support Ukraine's reconstruction, defense, and war-fighting capability. Provide more offensive weapons to go after military targets inside of Russia. Re-establish air-superiority and consider establishing NATO no-fly zones around civilian population centers. In addition to changing the military situation, strong moves like these will signal that the West is resolved to a degree that will dramatically raise the risks for Russia, ultimately prompting a recalculation.
Downvoting should be limited to text that detracts from the conversation, not used simply because the downvoter disagrees with what is written. (If you disagree, then reply with a rebuttal. Lazily clicking downvote helps nobody).
Going into Ukraine purely as a "defensive" effort would create another indefinite war. And maybe that's the right thing, but right now a lot of Americans aren't prepared to commit to that. They'll send money, and weapons, but not put people in harm's way without a clear indicator of what they have to do to get out.