I think that under your example, there are by definition no drawbacks.

If Ed is annoyed that everyone else has gone commie, then by definition we are not talking about your hypothetical (We didn't get 'everyone on the planet'). So we can't suppose drawbacks that involve 'someone not liking it'.

Generally speaking, a situation in which everyone freely decides to work together has no downside (except in odd cases like everyone deciding to work together to burn down all the plants on Earth).

If I were to look for a realistic problem -- other than probability, human nature, and logistics -- it would be the word "temporarily". I don't imagine that coming out of the universal accord would go smoothly.