Why are interracial marriages bad?

Neither, because not everybody in the world thinks the same way when it comes to interracial relationships. Some societies, cultures, families and individuals agree and disagree with it; so basically it depends on your culture, upbringing and beliefs on the subject it what decision you feel is correct. For example some cultures don't allow IR couples, does that make them bad people? No. Some cultures allow IR couples, does that make them bad? No. So it is good or bad depending on the person and the exact relationship.