This country started recognizing dual citizenship within the last ten years, when Obama was born it did not do so.
Dual citizenship is part of the diluting of American citizenship that the liberals have fostered upon us like anchor babies when it used to be that an illegal alien child that had been born in this country and abandoned was considered for citizenship under the Jurisdiction clause of the fourteenth amendment.
Can you point me to the law that started recognizing it? I'm pretty sure that the U.S. position all along has been that they don't encourage it but it certainly isn't illegal and isn't a threat to U.S. citizenship unless the person knowingly performs one of the recognized expatriating acts.