re: US needs to stop allowing dual citizenship, you are either American only or not.

Technically, the US doesn't recognize dual citizenship. They will treat you solely as a US citizen regardless of other citizenship that you may possess. This is one of the reasons why the US taxes its citizens on worldwide income. If you're coming into the country, a US citizen must use his/her US passport. However, they do not disallow you from holding citizenship of another country (like some countries do). The US won't force you to renounce citizenship of another country. They just ignore any other citizenship that you may possess.