Is it? Or is the goal to turn the people of Russia against the Russian government for putting them into this position, perhaps even triggering regime change.
Therefore, I believe there's reason to believe the West willingly allowed Russia to enter this war, perhaps with exact this goal: causing Russia to go broke (similar to what happened to the USSR in Afghanistan, which was also assisted heavily by the West at the time) over a gigantic conflict (and sanctions), forcing a regime change in Russia, finally, at the cost of a totally destroyed Ukraine. Maybe the West thought the cost (thousands of Ukrainians and Russian dead, two destroyed economies, another generation of people who can't trust their neighbours anymore, increased military spending) was acceptable?
Conspiracy theories aside, avoiding war at all costs by capitulating to the aggressor's demands without a fight is not a sustainable approach.
Sure, Russia was strongly and publicly opposed to Ukraine joining NATO, to the point of threatening war over it… but that isn't their decision to make. Russia is still the unjustified invader here and the only one at fault—not Ukraine for seeking NATO membership or the other NATO members for considering the application.
Putin was basically asking NATO to harm itself, there was no way anyone was going to take that seriously.
With all due respect, there was nothing to negotiate. Practically every world leader came to Putin's virtual doorsteps and tried to negotiate. Olaf Scholz even hinted at the fact that Ukraine wont be able to join NATO anyways bc of various reasons. But none of that helped. Putin has nuclear bombs. If we were to bend to his will bc he threatened to invade Ukraine, then we might as well pack our stuff, bc he has bigger threats. I can already see the messages on our post-nuclear-winter internet "Well, Proto-Putin threatened to start a nuclear war. The West had every chance to just allow him to crown himself Godking of Earth. This was the West's fault!".
I'm sorry but your worldview is cynical.
> so I am convinced the war could have been stopped,
Yes, by Putin. But he didnt. And that's somehow the fault of the West, I guess?
Vladimir Putin: I am absolutely convinced that Ukraine will not shy away from the processes of expanding interaction with NATO and the Western allies as a whole. Ukraine has its own relations with NATO; there is the Ukraine-NATO Council. At the end of the day the decision is to be taken by NATO and Ukraine. It is a matter for those two partners.