The whole premise of Western approach is that Russia is doing all of this unprovoked. If that is the truth and nobody attacks Russian soil, there is a small chance that Russian population can see their folly and realise that nobody on this planet has an interest in their shitty swamp. I say small, because I don't think that nation is the smartest cookie in the jar to begin with.
The second anyone not Russian touches Russian soil, you are literally turning this into The Great Patriotic War 2.0. We don't want that. I mean, not unless we actually intend to break Russia like Germany was broken. Completely devastate the entire nation and occupy them for oh, 50 years or so. Again, nobody on this planet actually wants to live in that shitty swamp. So, let's not do that.
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Actually, considering how Ukraine fights this war, a demilitarized zone of 10-20 KM seems fairly simple to enforce.