No basis in the Constitution for his decision? What about this?
Article IV, Section 2.
No Person held to Service or Labour in one State, under the Laws thereof, escaping into another, shall, in Consequence of any Law or Regulation therein, be discharged from such Service or Labour, But shall be delivered up on Claim of the Party to whom such Service or Labour may be due.
Can congress override this requirement with legislation?
Taney thought if he decided issues not before the Court to resolve the slavery issue once and for all that he would bring peace to the dispute between North and South.
That sounds like a very plausible conjecture, but so far as I can tell, the actual constitutional law is on his side insofar as it deals with the specific case of Dred Scott.
People might argue that Scott wasn't a fugitive, or that he didn't "escape", but if the intent of the Constitutional compromise about returning slaves to the person for whom their labor is due is to return slaves to the person for whom their labor is due, then it is sophistry to argue that it depends on how they "escaped."
It's not pretty, but it is legally and logically consistent so far as I understand the intent of the Constitutional clause.
Sorry, but I don't have time to debate with someone who actually thinks Dred Scott was correctly decided.