What were some of the founding fathers' concerns with the inclusion of a "Bill of Rights"?

See explanation.

Explanation:

Federalists (those who did not support the Bill of Rights) mainly argued that such a document was entirely unnecessary.

Federalists felt that the Constitution's specific provisions limited only the government, and in no way limited the people. They also felt that anything which was not specifically mentioned in the Constitution as a responsibility of the federal government would automatically become a responsibility of the state governments or a right of the people.

The Federalists did not want to limit the rights of the people, they just felt that the Constitution already guaranteed those rights set out by the Bill of Rights and that the Bill of Rights, therefore, was an unnecessary addition.