During the time of old, intermarrying took place. But as time passed by, it ceased to take place. Intermarrying is something that is kicked against according to the christian faith. God's instructions and commandments are things that we should at every point in our lives be found in our hearts.
As christians our culture differ from the culture and norms of the society. So because a particular ethnicity agrees to it does not mean we as christians should agree to it. The bible said though we are in the world we are not of it. We are not to be in conformity with the standards of the world.
Even in the world of science it has been discovered that marriage and relations that goes on between people with the same blood can cause harm to the body; thereby leading to sicknesses and diseases. But when this happens to people of completely different family genes, the children the produce are safe from such.
Leviticus 18:6 - None of you shall approach to any that is near of kin to him, to uncover their nakedness: I am the LORD.
The bible says it expressly. Practicing such act is an abomination to God. We should not let ourselves to be deceived by anyone.