An interesting analogy - and similar to one I thought of earlier but decided not to post.
Let's say when you were at school a bully decided to pick on one of your mates and take his pocket money - a common thing in the 70's and 80's. Would you stand up for your mate or would you allow the bully to prevail because you were scared of getting punched in the face ? And I know it's a pathetic example !
For me, the answer is ALWAYS stand up to the bully .... you're next !
I can see it now. In a few weeks, Johnson will emerge, waving a piece of paper, declaring that 'Mr' Putin has promised to jolly well not invade any more countries, meaning we can buy his oil again and welcome his countrymen back into the International Fold.