If you are interested in learning what drives Supreme Court justices to make "new law" and uphold certain decisions, read the book "Scorpions". A lot of their important decisions, such as Brown v. Board of Education, are driven by global perception. The Brown decision was not driven by the desire to help people of color, or by "social justice".
The Nazi's adopted a lot of the tactics Americans used to suppress, control, and punish people of color; especially in the South. This became common knowledge during the Nuremberg trials. Brown was decided a few years after the end of the Nuremberg trials. The U.S. Supreme Court wanted to "clean up" the United States global image, and "show" they had nothing in common with the Nazi regime. Brown gave them the opportunity so say, "see, everyone in America is treated equally".
There is a reason why decisions such as Brown and Roe were not codified into federal law.
Also, a lot of decisions that were originally decided to suppress the rights of certain groups were later used to benefit those same groups, such as the "Korematsu" decision.
> FDR tried it
He did. And it achieved the desired result!
I think you might be the one who needs to read a history book. I highly recommend Noah Feldman's Scorpions: The Battles and Triumphs of FDR's Great Supreme Court Justices.
Actually, as a threat, the court-packing scheme worked great! It successfully put an end to the "freedom of contract" theory that the conservative court had been using to strike down state-level labor laws. Minimum wage, over-time, mandatory breaks, that kind of stuff. And forget about Federal-level labor laws. That wasn't remotely feasible prior to the court-packing scheme.
Roosevelt may have spent political capital on the court-packing scheme, but it was capital well-spent.
If you want to learn more about the Depression-era Supreme Court and the interactions between the Roosevelt administration and the Court, I highly recommend Noah Feldman's book, Scorpions: The Battles and Triumphs of FDR's Supreme Court Justices.