Plain simple - it is Putin’s actions, not any response to them that risks WW III, if that’s what Putin wants now. Otherwise, it WILL come, due to no western military response to Putin now and it would be only a matter of time.
If I understand that correctly, you're suggesting that any "western military response" to the Ukraine invasion carries less risk of initiating WW III, than no military response. If so, that's a very entertaining point of view...
;>)