The correct response is: Northern states viewed enslaved people as property, thus they believed that enslaved people should not be counted as full citizens.
This perspective was part of the broader debate over representation and the status of enslaved individuals in the context of political power during the drafting of the U.S. Constitution. Northern states were concerned that allowing enslaved people to be counted as full citizens would disproportionately increase the political power of Southern states in the House of Representatives.