That is very different from just viewing slaves as property. It was an attempt to embed racism into the Constitution itself, which had never mentioned the subject. Or for that matter, slavery itself. The Founders very carefully referred to the institution with euphemisms rather than pollute a document enshrining freedom with the word slave.
More like the Constitution did not preclude it.
Taney ruled that freed slaves could be citizens of their state, but the states had no power to make them citizens of the United States. That took a constitutional amendment.