Same race marriage should be banned because procreation without adaptation is harmful to society, to the parents and child, and to the gene pool. Without interracial marriages, the phenotype of the population remains the same, leaving this population stagnant and with a lack of genetic development and adaptation. This means that children from same race marriages add nothing to society while using up resources and part of the workforce by taking time away from the people that need to take care of them. In order to promote continuous adaptation of the whole of society, all marriages must be interracial and anything else should be illegal.
Interracial marriages also create a new generation of people who are not as prejudiced against people of other races because they gain tolerance for different races and cultures since they have been exposed and are apart of more then one. If someone is raised while experiencing and being a member of one group and one group only, when exposed to a second group it is likely they will be prejudiced against it. If someone is raised in two different groups, when exposed to a third they are more likely to be accepting of it because they wont think that there is only one right group, but that there could be many right groups. If interracial marriages had been the way everyone was raised for the past 100 years, the Civil Rights movement would have been much less painful for society in its entirety. Racial tension in the present also would be much more relaxed allowing for a more peaceful, tolerant and positive society.