Sorry, but there is no way in hell a European wouldn't know they have dual citizenship by being born in the U.S. And there's no way they wouldn't have renounced it in all this time unless they saw that citizenship as a benefit that outweighs the costs, or at least as a potential benefit down the road.
This article imbues Accidental Americans with the stereotypical dumbassery of I-Am-A-Real-American's in an attempt to get me to sympathize with people who don't want to pay taxes.
Edit: added Hulk Hogan entry song reference for clarity