I don’t believe the Founders were stupid at all. They originally would have allowed naturalized citizens to run for President, and then increased the restriction to being born a US citizen. That is a low threshold, as is being 35 years old, but they actually believed the people should get to choose...
And here is a quote from the DISSENT in WKA (1898):
“Considering the circumstances surrounding the framing of the Constitution, I submit that it is unreasonable to conclude that “natural-born citizen” applied to everybody born within the geographical tract known as the United States, irrespective of circumstances, and that the children of foreigners, happening to be born to them while passing through the country, whether of royal parentage or not, or whether of the Mongolian, Malay or other race, were eligible to the Presidency, while children of our citizens, born abroad, were not.”
So you think they would have approved of birth tourism?
If you believe that, then it isn't the founder's stupidity I would be concerned with.