In an event it changes the matrix of the entire European Area, Russia can be basically blockaded if needed if they join. When is the "CRAZY MAN" going to realize he has made a grave error? Negotiations in the very beginning, BEFORE any military action may well have given Russia the sense of security they are looking for. Now with Sweden and Finland joining, Russia is going to bordered by NATO nations on almost their whole Northwestern Border.
^^^^This. Nothing but this^^^^In addition, while Ukraine was hardly a perfect country politically (which country is), it was slowly moving toward a functional democracy with rule of law. Putin could NOT tolerate that on his border.