When you take a look at maps showing how parts of big cities are dvided between people of different passions and interests, you will also be able to see how different we all are (attachments 1~3). Then, if you try and imagine this kind of diversity on a bigger scale - country-wide scale for this instance. You will have no doubt that there's nothing like homogeneous nation. In my opinion it's not only the origin of a person that matters but also the values they represent and those differ, no matter if nation is build with only one nationality or fifty of them.
Having said that, let's wonder for a second, what would happen without a government? It's highly likely that the more aggressive groups would eventually devour the smaller ones. In other words, we could suppose that there would be an anarchy from which we would end up with a regime. However, we know now that sometimes it takes one person to change the world, so what if those people were in the groups that wouldn't win because they were smaller? We could lose potentially great ideas and people!
Now, a good government ought to provide good environment for development to every single citizen. We know that it never works perfectly, but good democratic system can, theoretically, provide great leaders and amazing representants of every single of those groups. In a perfect world, in a democratic country, we have representants for all the social groups from a country and therefore, we can build an average best version of our future based on the consistency of the society