In today’s less racist world, we tend to see the decision in Dred Scott as a terrible decision because of its racist aspects. However, these aspects of the decision were not the most controversial at the time and they were not the worst part of this decision from a legal point of view.
At the time of the Dred Scott decision, most white Americans would have readily agreed that African Americans were not entitled to be considered as American citizens who had rights that white people had to respect. After all, if people really believed in racial equality, they would have been very hostile to slavery. Most Northerners were not abolitionists. They did not tend to think that blacks were equal to whites or that slavery should be abolished in the places where it already existed. They did typically want to prevent slavery from spreading, but not to abolish it where it was. For these reasons, most Northerners would not have been terribly disturbed by this part of the decision.
However, Justice Taney then went on to write a sweeping opinion that touched on issues that did not even need to be raised in this case. This is why the decision is legally poor; the Court went out of its way to rule on an issue that was controversial and did not need to be raised. Taney ruled that Congress could not make any laws respecting slavery in the territories. This caused tremendous worries in the North because it would conceivably allow slavery to spread to every territory that was not yet a state. This would have allowed the slave economy to dominate the country, reducing the chances for Northern whites to prosper.
Thus, Taney’s decision was a poor one even by the standards of the time. Today, we think it is horrible because it was racist. When it was written, it was a poor decision because it needlessly caused greater tensions between the North and South.