Most countries are relatively homogeneous. Some of the most homogeneous countries are the most horribly governed: North Korea, Albania, Algeria, Haiti, Lebanon, Libya... the list goes on and on.
How do you consider Lebanon to be homogeneous? The religious divide there is so deep and long-standing that it is enshrined in law, with power in the government divided along confessional lines.
Yes, Lebanon is a bad example. I was going with the fact that most people are technically Arab, ethnically. But you are correct, that doesn't have much bearing on the actual divisions in the country.