We would be heading into indirect, leading to direct, conflict with Russia.
I know western forces have been much diminished since the height of the Cold War, but Russia's have been even more so. Add the fact that there's a helluva lot more countries in NATO than there were then. Personally if it ever came to a fight I think it would be pretty one-sided. One can imagine the Russian forces defecting en-masse, now they know all about our way of life, many of them having tasted it.