Because the United Nation's aim is to maintain peace by secular cooperation and if they were to prove to be successful the Watchtower claims and status would be diminished since it tells the world (rather feebly) that it alone has a magical solution.
In a religious cult it is a good thing to have 'goodies' and 'baddies' then the tiny minds of the believers know who to cheer and who to boo. Visible enemies make your spritual cause seem more real.
God and Jesus are constructs of the human imagination and therefore cannot hate or love.