lol, there are too many conflicts and dislikes. Look what happened to Yugoslavia? The only way that a world state would work is if you were to first get rid of all that rivalry, hatred, and conflict (religious, ethnic, ideological, etc). Even still, when the world is so split up on how a country should be governed (Socialism in Europe, Communism in many place, whatever the heck you call America - I will not get into an argument over definitions), that it would never work. Regions would all want to be governed whatever the prevailing way in that reason is and it would fragment. As ideal as it sounds (kinda like Communism did), it just would not work. (even if you went through mass killings and reeducations like the USSR)
Best thing to do IMO is for us all to stick our nose out of each others business and try to work together...not to make others work for us *cough* International law *cough* US in Iraq *cough* Russia in Central Europe *cough*
Sure, some international laws are needed to ensure that everyone does stick their nose out of everyone else's business, but other than that, I think we should let Iraq do what Iraq does, China do what China does, Russia do what Russia does, the US do what the US does, etc. (I am talking about governments, not individuals getting involved in humanitarian work or charity)