Why was popular sovereignty unconstitutional according to the Dred Scott decision?

The Dred Scott decision, delivered by the U.S. Supreme Court in 1857, ruled that popular sovereignty—the idea that the settlers of a territory could decide whether to allow slavery—was unconstitutional. The Court argued that the federal government had no authority to regulate slavery in the territories, as it violated the property rights of slave owners under the Fifth Amendment. Consequently, the decision effectively invalidated the principle of popular sovereignty by asserting that Congress could not exclude slavery from the territories, thereby reinforcing the legal status of slavery in the United States.