I can only begin to imagine the scale and scope of the issue. Humanity is not nearly close enough culturally where such an organization can realistically be suggested.
Sorry if this is naïvety and I can't speak for anyone other than myself but at least for me there's an irrational "love" element that I cannot silent. We fight for political control but my "tribe" is the entire country, not my region. Personally, the day I start talking about how it is economically beneficial to stay in the union is the day I start preparing for the union to dissolve.
I quite like Neal Stephenson's idea in Diamond Age of some sort of enforceable world economic protocol.
Why would anybody be happy letting people with such fundamentally different belief systems make their rules?
Of course this has the potential for conflict as well.
In the mean time we seem to be on a regressive path and for now further unification is over the horizon. The cause - at least, in my opinion - was that the unification attempts that were made were made in bad faith, for short term economic reasons rather than for long term stability reasons.
For example, the US was instrumental in enacting the UN Single Convention on Narcotic Drugs, so a government that I don't get to vote for had a direct influence on the laws of my country (UK).
If, for example, Asian and Middle Eastern countries influenced the law of this hypothetical world government in proportion to their population, then the UK might be compelled to execute violators of the drug laws you refer to.