There are 3 Branches of the U.S. Government and birthers reject all three. Birthers reject the rulings of the courts; the same courts which have ruled against or refused to hear the birther cases of Orly Taitz. Orly Taitz has even been fined by a Georgia Court for bringing frivolous cases. The U.S. Supreme Court has rejected her attempts to present the case before it. Birthers reject the executive, claiming that he isn't "their president," as if they actually have a choice to reject a democratically elected U.S. official. Finally, birthers are against the legislative branch of the U.S. government; not because the legislative branch has legislated anything concerning the birther issue, but because the leadership of both parties have denounced the birther issue as nonsense.
So, what we have here is a movement as dangerous as the sovereign citizen movement. We have people who are not doing anything illegal yet, but who reject the American government as legitimate. Homegrown terrorism is often based on believing that the government is illegitimate - this is not a trifling matter and Americans should be wise enough not to cling to such nonsense. But the even more dangerous thing is that we have a party (the GOP) which is showing an inadequate amount of leadership on the issue. The Republican leadership has said that they believe Obama is the legitimate president, but even John Boehner, after stating that he believed Obama was a legitimate citizen, thought it was necessary to state that it was not his job to tell his constituents what to believe. So, is he or is he not a leader in America? Leadership is a prerequisite for being a leader, that means that you have to be willing to unequivocally reject a popular idea which is wrong and possibly harmful to the United States.
And now we have Donald Trump, who has managed to catch the attention of the birthers in his potential bid for the presidency. The simple fact that the birther issue is still a viable issue in American politics shows what a dangerous issue this is. Even though nearly ever sensible American has rejected the idea, there are nuts out there who really believe. And it may be this issue, not the budget deficit or any other substantive issue, that helps decide the 2012 election. I'm not saying that a birther will win an election, but it is going to affect the general conversation within American politics throughout the campaigns. The 2012 elections are still far off, so potential candidates are still willing to spew extreme garbage. If this issue persists then it is dangerous to democracy in America. If this is the focus in the last few months of the presidential campaigns - then I will be really scared for this country.
Oh, and I forgot to say - ignorant popular political rhetoric is un-American.