I'm amazed that anyone here thinks it is a good idea or even any of our business what happens between Ukraine and Russia.
I didn't say it was a good idea, I just said I could see what was coming down the road. I actually don't think anyone in the west cares enough about Ukraine to actually go to war, even if it were a good idea. I suspect we are going to let Russia take at least some chunks of Ukraine if not the whole thing. It is what it is. If I were going to bet I'd say Russia will look back to finish the job of conquering Georgia next. After that things get stickier. If Ukraine falls and Belarus is already basically under control that puts Russia right on the borders of Poland (former Warsaw Pact) and Lithuania, Latvia, and Estonia (Former SSRs). Those countries are all NATO members, and Lithuania and Latvia have large Expat and ethnic populations in the US to raise a fuss, as well as US trained and educated people in positions of power in their respective countries. I suspect that even a "minor" incursion in any of those countries would be met with US military force. I don't know if Russia believes that though.
That also doesn't take into account that even if we want to stay out of the Russia-Ukraine thing, accidents happen and there are a lot of US and Allied troops and equipment in close proximity to where the fighting will be. To quote "Hunt for Red October"
It would be well for your government to consider that having your ships and ours, your aircraft and ours, in such proximity... is inherently DANGEROUS. Wars have begun that way, Mr. Ambassador.
We got closer to shooting it out with Russia in Syria than I think most people realize.
And as previously mentioned letting folks just conquer territory they want sets an example, one I'm sure an aggressive China is paying attention to. Much like Ukraine, I don't know if we are willing to go to war over Taiwan (whether that is a good idea or not is a separate discussion) But we have Mutual Defense treaties with The Philippines, South Korea, and Japan, all of which are in the crosshairs if China starts expanding territory instead of just influence.
Do all of those things mean war is a good idea? No. But it's worth being aware of the shitstorm coming down the road so we may try and dodge at least some of it. It is in the US national interest not to be a second or third tier country in a world being carved up by Sino-Russian expansionism.
Perhaps we'll get lucky and find out that Kiev managed to keep an old Soviet nuke, and they'll return it to the Kremlin.