What you describe is not dual citizen by birth. It is registration as a Citizen by Descent. Registration as Citizen by Descent is not the same thing as "Any third generation person born in America to two parents who were born in America [and grandfather was a Euro citizen]
is a dual citizen."
While you are a natural born citizen of the US, I think your actions demonstrate a lack of resolved allegiance to the US.
What you describe is not dual citizen by birth. It is registration as a Citizen by Descent. Registration as Citizen by Descent is not the same thing as "Any third generation person born in America to two parents who were born in America [and grandfather was a Euro citizen] is a dual citizen." Well certainly very interesting that you think all of that. As to the one Euro country I know about, clearly wrong under their law--I could go there and vote with my US Passport; I just didn't know it.