Interesting. I suppose some of this depends on how one classifies a Ukrainian victory. What is the Ukrainian victory the States don't want in your opinion?
I think it's like most things that most people want - that at some point a magic fairy will come along, wave a wand and turn a messy, difficult situation into one that's great, and doesn't have downsides.
I've
genuinely not met, or heard of, any of the western supporters of Ukraine in Government who are wobbly on the restoration of Ukrainian territory under a democratic government that is free to choose it's affiliations. Everyone is solid on that - the problem is the potential consequences of the
means of achieving that.
There are, in effect, three fears that hold people back from giving Ukraine the tools to accomplish a full-fat military victory through physical domination of the battlefield:
That Russian central state power/governance will collapse, and that Russia will become a giant failed state with 6,000 nukes and an endless supply of would-be former vassal states/territories looking to get out of its orbit.
That Grey-zone/conventional Putin would be replaced Putin would be replaced by nuclear Putin - whether it's him or the next guy is irrelevant.
That Russia will be so politically and economically defeated by such an outcome that it will become an outright vassal state of China. China on the Arctic Ocean and the Polish border does
not appeal.
The fundamental problem is that there seems to be very little space between an outright Ukrainian victory with Russia expelled from all pre-2014 Ukrainian territory, and some degree or combination of the above happening.