The USA allows dual citizenship, but disapproves of dual citizens assuming policy-level positions in foreign governments. ("Disapproves" here means that the person may, but not necessarily will, lose the US citizenship.)
I understand apprehension about dual citizens serving as government ministers and suchlike, but shouldn't we be concerned about them serving in our government, rather than in a foreign one? I'd be worried about having, for example, a Secretary of Defense who is a dual US-Saudi citizen, but why should I worry about Saudis having a Secretary of Defense who is a dual US-Saudi citizen? That's their problem.
For the record: I have nothing against dual citizens and am planning to become a dual citizen someday. I also don't think that dual citizens should be automatically prevented from holding high government positions. The voters, however, should have the right to know about politicans' dual citizenship, and to question their loyalties.