The issue it seems people are overlooking, whether or not Ukraine needs to be saved or protected, is Russia very likely has the ability to reach back. Other countries in all the recent past conflicts never had the ability to project power beyond a neighboring localized region. This very much has the potential to not be the one sided fight that was often the case in other recent history.

Even without threatening full fledged MAD, Russia could put NATO countries into a hard economic freeze by going after vital but soft infrastructure. Petroleum production is an obvious one, electrical grid is also undefended for the most part, and then international shipping is quite vulnerable. Mess any of those up for long enough (if not all of them), and the populace here is going to suffer a lot of difficulty in going through with this particular fight. It's not going to be fun if the power gets knocked out half of the time and you can't fill up your gas tank due to either cost or unavailability. Such things would be disruptive as hell, cause hardship, and will end up tying national guard or reserves just to keep watch in our own countries.

So the wildcard in this thing outside of the context of risking MAD is whether or not we can fully deal with Russia's navy and special forces. They don't need to occupy or control anything, they just need to be able to damage that which we depend upon.

So this thing has the potential to open up a huge can of worms, and do we want to deal with that?