Is 14 years really that substantial? The way people go on here about potential foreign allegiance, I highly doubt the anti-Cruz-birthers would ever agree to a mere 14 years residency to qualify for President. They would probably demand no one spent more than one consecutive year overseas. If someone was born in Texas, then moved to Britain for 40 years, then came back here for 14 years and ran for President, under your interpretation of "intent," the founders should've been totally paranoid that person was a foreign agent. Yet they left in this relatively minimal 14-year requirement for U.S. residency.
The lifespan was shorter then and it was a substantial portion of a life. That is the decision they made. There are letters in which they discussed the requirement between themselves.
There is additional information on many sites as to the reasons 14 years was chosen. One site with good references is: http://birthers.org/USC/ArtIIS1.html