Why would someone be against the ratification of The Constitution?
People were against the ratification of the Constitution because they believed that it would not be very democratic and that it would be too likely to cause the rights of the people to be infringed upon.
Under the Articles of Confederation, the states had all the power. They typically had very democratic governments. They also tended to have bills of rights in their constitutions.
The Constitution proposed a system where the national government would have much more power. The national government would also not be very democratic because only the House of Representatives would be directly elected by the people. Because of this, and because of the fact that the federal government would be located far from most of the states (sort of like how Britain's government had been far from them), they felt that the new government would be likely to ignore their desires and/or would be likely to infringe upon their rights.