I hate to use the word idea for something that lacks any actual backing thought. This idea crops up every now and then among technologists who only experience nature between car and building, and is especially popular in Britain and western Europe, where no one would have to change their habits or language if this nonsense were put into place. A few things technologists do might improve, but all other parts of life would be thrown into unnecessary, lasting chaos. This idea is ultimately nothing more than selfishness among Asperger's types who never consider other people.
There are thousands of reasons why a single worldwide time zone is a massively bad idea. I'll restrict myself to one: in such a world, where would you put the international date line? With the current, well-working system, the line between today and tomorrow is drawn though the Pacific Ocean in such a way that no country or economic zone is itself divided into today portions and tomorrow portions. With a single time zone world, that line becomes the GMT line, which would place one part of England and indeed of London into today while the other half is in tomorrow. Not to mention dividing France, Spain and portions of Africa into two days. Try planning your meetings around that.
You don't seem to understand that the time zone system was made possible by technological changes. It's not some baggage that we carry from the caves, it was invented in the 1870's when transcontinental railroads in Canada and the US had to come up with reliable timetables. The technology that allowed near-simultaneous setting of clocks hundreds of miles apart was the telegraph. Before the railroads needed time zones, and before the telegraph made them possible, all time was local and was generally based on the position of the sun locally.
The imposition of a single worldwide time zone would require a complete break with parts of language and literature, in every human language. Words like dawn, noon, and midnight describe the position of the sun, and today, in every language, also describe roughly the same time of day. Dawn is about 0430 to 0730, depending on season, in the populated temperate zones, and that is true in all latitudes of those temperate zones. In your world, dawn would be 1230 to 1530 in one place and 2030 to 2330 in another, so the word dawn loses its current meaning to describe a time of day. Books written before the start of your brave new world would all use the old meaning of dawn and would assume the reader knows that dawn-colored sunlight is a rosy pink.
To schedule intercontinental meetings, I rely on timeanddate.com and its cross-time-zone scheduler. If that didn't exist, I'd have to do a little math. All airlines already compute their schedules internally in terms of GMT, then publish departure and arrival times in local time. It really isn't hard to live in a world that we have very wisely divided into naturally-occurring time zones.
