Because it serves no purpose but strife, hatred and intolerance of other human beings?

Those things existed before and without nations. Civil wars happen despite the participants being of the same nationality. A country is (usually) simply a label for a group of people with a shared culture, language, mindset, etc. Removing those labels is a naive attempt at achieving some global utopia filled with uniform drones.

And how would doing such thing stop those who hate and are intolerant?

It would reduce the justifications such people have for their heinous activities.