I thought that was the whole reason that the term "natural born" is even in the Constitution. So as to prevent anyone that may have dual allegiances or strong allegiances to foreign countries that may interfere with their ability to lead the US. The term "natural born" is used to mean a singular allegiance to one and only one nation. Dual citizenship contradicts this.
I may be wrong, but I don't think you know very much about how dual citizenship works. You're presenting the situation as if Obama had actively gone out and sought Kenyan citizenship when he was 21, or something along those lines. That's nowhere near the case.
But even if that were the case, you would still be wrong. I'm pretty sure (and a quick internet search verifies) that the phrase "natural born citizen" now simply means someone who is born a citizen of the U.S. There are possible interpretations whereby it might mean something slightly differently than that, but if a case went before the Supreme Court that is almost certainly how they would rule (in my humble opinion).