I do not have a problem with it. But assuming anyone in any movie is only cast "Because they are the best for the part" is very naive.
First of all who is best suited for any role is completely subjective regardless of their race. But more important than that , This is Hollywood! More and more the studio execs are making decisions based on market research and demographics. They are looking to make the most money possible. Never assume that on a property like this that the director has final say. The studio have huge influence on casting. They probably had finalists which they approved and vetoed certain actors. Maybe the actors were of different ethnicities. But the idea that its as simple as "Best for the Part" does not understand how the business works when so much money is being put into these things.