Other than the aforememtioned social security/welfare state reasons, is there any rational reason why the US needs to increase its population?
On a economic level, people are wealth. Any conservative or libertarian economist will tell you that. So the question becomes, why does the US need wealth?
But the most rational reason of all is because God has commanded us to do so.
Incidentally, "overpopulation" is a myth.
Lets say we give all 6 billion people on the planet 1,000 square feet each, did you realize that they all would fit very easily into the state of Texas (with over 1,300 billion square feet left over!).
• Texas has 262,015 square miles of land
Which equals 7,304,558,976,000 square feet (262,015 x 27,878,400*) in Texas
• Each person gets 1,000 square feet of land
• The world population is currently almost 6 billion people (as of 1999)
• 6 billion x 1,000 square feet per person equals
6,000,000,000,000 square feet needed