'Cause that's the way the founding fathers wrote the Constitution. They provided the electoral college and Congressional certification as protections. If that failed, the Constitution lays out a process to get rid of a sitting president, impeachment.
Perhaps if birth certificates were common in the late 1700s, the founding fathers would have required a candidate present his to prove that he met the citizenship requirements, but they didn't.
But these protections are not a low thresholdthey are quite high, at least as originally intended. Our problem is that a speaker of the house, and some recruited gangs and mobs, has stretched her hairy arms way up and bent the thing down to a very low level, so that scoundrels and rapscallions and low down criminals can scamper right over it.
Why should we accept such artificial standards?
Why do you anti-birthers not consider the security of our nation to be a very high priority?