The use of a global currency will be the starting point of eliminating suffering in the world.
Still far from the starting point of eliminating suffering in IMO, One currency usage has advantages, but still has it disadvantages and one majorly being
Loss of monetary policy: If the whole world used one currency, there would be no way for individual countries to control their own monetary policy. This would make it difficult for countries to respond to economic shocks or to achieve their own economic goals.
sourceThe world will get there someday, and maybe by then the loss of monetary policy will no longer be an issue.