Answer:
Hamilton thought it was too unnecessary. Many of the land/territory may not be used because of how vast it was. Also, Jefferson was sort of a hypocrite. He had a strict view of the constitution and believed that the president didn't have any powers that weren't implied in the Constitution. Buying foreign land wasn't in the Constitution, yet Jefferson still tried to make the Louisiana Purchase by buying it from France. Also, the Louisiana Purchase may seem unconstitutional and there would be too much land to govern.