Well, ultimately if Russia wants to invade it can, but the West needs to make sure there are serious consequences. Economic, diplomatic and whatever.
Do you really think Putin should be able to invade a sovereign state of 40 million people and everyone should just go "Hey, that's cool bro".
I should imagine you'd feel quite different if a dictator's troops were queuing up to invade your 3rd rate country.
Where did I suggest that we just 'let Russia do as it pleases'? I just don't think every solution to a problem is one that involves war and bloodshed
Economic punishment would be the real stinger. Not a bloody war throwing bodies at each other
Russia
needs 'The West'. It's economy is heavily dependent on European customers for their products (eg oil). Europe can survive without Russia but Russia cant survive no longer being a player in the global marketplace
There is little appetite in Russia for an invasion of Ukraine. It would also cost a shit load of money they don't have, not just in trying to take it but in keeping it. Add to the fact if they did, Europe sure as shit wont be doing business with them.
If simply agreeing that Ukraine wont have NATO military and bases and that avoids a war - then just fucking do it. Sit at a table and hammer out an agreement with the knowledge that not everyone is going to get everything they want but everyone can walk away with something they want. Then everyone can save face for their respective audiences back home.