>I think the argument against promoting an existing language as a 'global' one was that it would tend to give an unfair advantage to its native speakers.
More than that, Esperanto would be politically neutral. I think this is no longer very relevant in today's World.
The other major advantage of an artificial language is its simplicity - no irregular verbs, etc.
Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)
