How many Congressman have brought up laws that turned out to be unConstitutional? Do you think it never happens?
I don't think you are comprehending the point. Let me try to clarify again. It is well known that congress cannot pass any ex post facto law. If a congressman attempted to pass an ex post facto law, it can be reliably assumed that every other congressman would tell him "No, you cannot do that! The constitution does not allow you to do such a thing."
An attempt to pass an ex post facto law would not even get introduced as a bill, let alone make it into a committee hearing, because everyone would shoot it down as being unconstitutional the minute it was brought up.
Now, consider that if everyone understood that birth within the boundaries makes a person a "natural born citizen", the very instant someone tried to pass a law denying this fundamental right to the children of foreigners, every member of congress would have stood up and said "You cannot DO THAT !" It would not have even been introduced as a bill, and it certainly would not have been sent to a committee for discussion.
It was not dismissed, it was accepted as a legitimate bill and referred to the committee of the judiciary. If your theory was correct, it would have been unthinkable to even look at the idea.