That FDR won doesn't mean the outcome was wrong. Sometimes good things are achieved by bad means, and the Supreme Court had arguably been guilty many years of attempting a certain philosophy. O.W.Holmes: "The Fourteenth Amendment does not enact Mr. Herbert Spencer's Social Statics." Whether court packing was also responsible for "the switch in time that saved nine" is also contested. Regardless it's been a very long time, and to uproot it will prove the conservatives have their own cynical ruthlessness re stare decisis.
Uygur's right on re hypocrisy--but faults the Dems for not doing the same? I think Obama can use either outcome as a podium issue: "I was right" or "the Supreme Court hates sick children." If the law fails, Congress is also defied, and it seems to me a lot of people will be hurt, plus a lot of other important laws will become suspect--this benignly named Commerce Clause power has been huge for 75 years, underpinning all from economics to criminal law to civil rights.