Stare decisis true, but the Sct does overrule itself. Two words- Dred Scott.
Two words - 14th amendment.
The part of the Dred Scott decision that actually affected the person, Dred Scott, was constitutionally sound. Under the constitution (due to compromise to ensure ratification), slaves were treated differently and individual states have never had the power to grant citizenship.
What makes the Dred Scott decision so notable is Taney's idiotic decision to editorialize and say that blacks were inferior to white and so forth. Apparently he had hopes that this would end the slavery debate once and for all.