This is just a starter list to get you thinking.
"Advantages" of less cultural diversity:
fewer wars
one language

"Disadvantages" of less cultural diversity:
one language
more wars
narrower spectrum of human "experience"

Yes but you can't deny that cultural diversity is ruining the lives of millions (sudan, tibet, the middle east in general).

Where as if they were all assimilated into one culture the violence would die out. Then the people would be more likely to be successful in their endeavors throughout the world.

However, while cultural diversity makes the world a colorful and exciting place, it also makes it a very scary place sometimes. Because cultural diversity is why people fight wars. They fight for land, autonomy, rights, religion. Many wars come from people believing that their culture is better, and therefore, they must impose it on others. (Imperialism) Other wars come because people feel that their culture is being threatened. Sometimes it's in retaliation to imperialism, but other times it's just because a certain group of people believes that it deserves more room to practice their own customs. They might want their own country or governmental autonomy. And still other wars happen because the two groups just don't understand each other. Wars of ideaologies, especially dangerous because both sides believe themselves to be right, and are willing to fight to the end to make sure that their ideology wins out.

Even if everyone had the same culture, I'm sure there would still be wars. Because we're human. We always find something to fight about. Unless every single person on earth has the exact same thoughts and opinions, wars will happen. It's inevitable.

Personally, I don't want to see the day when every single person on earth agrees. That would be such a boring, pointless world.

Cultural diversity is a double-edged sword. It provides the world with color and beauty, but it's also what makes humans fight against each other most often.

I'd like to think that world peace is possible, but the truth is, it's not. Because we're all just too different. But I think that we should all just accept each other for our differences, and remember that everyone is human. That's how I try to live my life anyway. Other people don't, obviously, and although that saddens me, it's only human.


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And while the seagulls are crying,
We fall but our souls are flying.