The correct answer to this open question is the following.
Thomas Jefferson thought that if the constitution was not followed strictly, then, the federal government could increase its power and control over the United States citizens.
That was the main argument of the anti-federalists led by Thomas Jefferson. They opposed the federalist's ideas -led by Alexander Hamilton and James Madison- that supported a strong central government. Jefferson cautioned on the risks of a powerful federal government, that is why he and other anti-federalists considered the necessity of a Bill of Rights in the US Constitution.