What happens if everyone becomes rational?
We will turn Vulcan (star trek) and will have to deal fewer errands.

What will happen to our emotions, feelings et all?
We will become robots.

That will save Earth?
Who knows, it might. We will start using our consciousness. We will become unbiased. Emotions will have no role in decision making.

But what will happen to the division we have created?
Rationality will not fuel division. Since we will have no meaning or importance on attachment or emotions. We all will be two-legged walking animals.