Original Reason for Dual Citizenship
Many opponents of the dual citizenship have posited that loyalty is the main problem. History has it that the main contention against dual citizenship has a diplomatic origin instead. In the days of yore, the rights of a citizen entirely depended on nationality and sovereigns could do as they please with their own. With the then laws if one had dual citizenship protecting a citizen of one country potentially faced challenges with citizenship of the other. This then became an issue between sovereign nations and not the individual any more.