Debate: should English be the one and only dominant language?

Let me give you some background before we plunge into this very controversial question:
  
The Swedish nationella proven (national tests) are approaching rapidly. It's big, like really big. I guess you can imagine. This years theme is The possibilities of language and we can basically write about whatever we want to, as long as it's relevant to the topic. So I decided to write about the English dominance over the other languages around the world.

The problem is, I don't know where to start! Sure, there are pros and cons on every subject, this one's no exception. If everyone spoke English we'd all understand each other, and that would be great! But won't the other languages decline if English receives the spotlight in elementary school? What will happen to each countries national identity?

This is me, trying my hardest to find the answer!

So everyone, debate. Should the world convert into an English spoken one, or should each country preserve its own language and culture? Share your opinion!