But, that's immaterial. The fact is it is simply a matter of law. One can hold many citizenships. If the American with a British father were Jewish, he could obtain Israel citizenship too. And then if he moved to Canada he could get Canadian citizenship, and for $50,000 he could get citizenship in Belize, and for $300,000 he could get citizenship to Australia. Yes, some nations simply sell their citizenship. What can be done about it? If you look it up, you will find many stories about people who "collect" citizenships like others collect rare stamps.
Regarding the 'serving two masters comment---I would suggest to you that a person can't honestly serve as citizen for two countries at the same time--there is bound to be conflict and one of the countries has to be on the losing end. Consider a dual citizen of the US and Israel...would they vote to keep or eliminate foreign aid--the best interest of which country would be served? Or in the case of the US and Mexico, a vote comes up regarding the border--one is to keep it open and the other is to patrol and keep illegals out--would you feel comfortable with which vote?
Of course, it is too much to expect that we would have men and women in our government who has hormone levels commensurate with changing laws or making laws which would eliminate the possibility of dual citizenship; and yes, probabaly even the Constitutional amendment enacted regarding being born here--but even at that, I think it, too, has been bastardized by the 'living changing document' advocates!
Bottom line.....our corrupted politicians and bureaucrats will continue doing whatever they want in an effort to get 'everyone' to vote for them--America, as a nation, can go to hell in their book.