The fact is, no one can lead a nation while having to answer to another nation. Unfortunately, that's not true. I agree with you it is a bad idea to have a dual citizen as president, and I would certainly think twice before voting for a dual citizen. I did not vote for Tancredo. However, the fact is there is nothing in the Constitution prohibiting it.
That being said, we know Obama is NOT a dual citizen. He was born with dual citizenship with Kenya, but he lost it when he was in his early twenties, since he never took any action to retain it. We also know for sure he was never an Indonesian citizen, as to become one he would have had to renounce his US citizenship, and there is no record of him having done so.
"That being said, we know Obama is NOT a dual citizen. "
Do we? When he was born he was a British Citizen by birthright. Since he only claimed his Kenyan citizenship lapsed on his 21st birthday and the fact the Kenyan Constitution expressedly protected his dual citizenship with the UK until his 21st birthday, he was and still is a British Citizen unless he can prove otherwise. Some may argue he became solely a Kenyan Citizen, but if you read carefully, you will see this only applied to citizens residing in Kenya at the time of its independence.
You don't just "lose" your British citizenship. You have to renounce it after your 18th birthday. It's actually harder to remove British citizenship than it is U.S. citizenship.