I think, just as the previous reply said, stating just like that: "is it wrong to adopt a child...", the answer would be no. I think that it is not always wrong. But I think that one needs to go deeper into the question: maybe one should ask "when is it wrong to adopt a child from such different ethnicity...?"
I think that there are different components one needs to look at for the answer. First, who makes the decision?
When parents move to a new country, their children might easily feel estranged. The parents have to decide if it is worth it, for the child to live in a strange society. But it is their decision to make, as these are their children. Society thinks that parents have the power to make such decisions.
But with an adopted child, who has the right to make the decision? First of all, of course, the original parents. The child might have been given to adoption by the parents, because they live in bad conditions, or because they think the child will have a better future in a different place. Of course the parents could also have had no choice, or the child could be an orphan. If the parents gave the child away, what information did they have? Where they educated in all the problems that their child will suffer if it gets adopted in a different place? Did they hear report about how adopted children do in a new place? I think that often, those that have most right to make the decision, the original parents, are least informed.
Then there is the government or agency where the child is then placed, and the adopting parents.
There are also others who might think they have a right to speak. For example, we should probably listen to the opinion of adults who were adopted as children, and who went through the ordeal - what do they think. It is also not just the adoption of a child, but of the child's whole family - their children and grandchildren. We should probably also hear their opinion.
The state of the adoptive parents is a bit strange, because they make a decision in the name of the good of a child they don't have yet. And whose good should they go for? The good of the child that is currently in the orphanage, and who will maybe fare much better after having been adopted, or the good of the child they will have in a few years, and who might have been a happier child if it was adopted within the same ethnicity, same country, or might have been the biological child of the parents.
Another question is consequences. What are the consequences of the adoption? One consequence one hopes for is that one child will be better off. If its only other option was to remain in the orphanage, it probably is in a better condition.
But sadly there are other consequences. Money gets channeled to make the adoption possible. In cases where the child comes from a poor place, such money can provide an incentive so that more children are adopted, instead of staying with their parents. Money might be paid to mothers to "help" them during birth, before they give the child away. Or, mothers could be given a bit of money to live better after they gave the child away. And mothers might be persuaded to give their child away to a better and brighter future. In the worst case, children might also be abducted for adoption. In the end, an adoption might then lead to more children leaving their family for adoption. This is an unintended consequence of adoption - the idea is to make the life of the child better, and not create more problems for more children.
A site with good information on the subject, in case of international adoption is
http://www.brandeis.edu/investigate/gender/adoption/index.html
and especially, look at 'The lie we love': http://www.foreignpolicy.com/story/cms.php?story_id=4508
In the end, I think one can not say that it is wrong. There is a child who needs to be adopted, and it would be wrong to let it waste away in the system. But, one needs at the same time make sure that adoptions do not lead to more children getting to orphanages. One needs to help the families before the child is given away, and one needs to make it clear to parents before they give the child away what the consequences are, and that the child will suffer from their action. The money that is used in one adoption could easily keep 10 children in their families, and one needs to make sure that it is not used as an incentive to take 10 other children from their families.
