Court-packing strikes me mostly as a comforting fantasy for the Left right now. It’s a way of consoling themselves over the likely emergence of the most conservative Supreme Court majority we have had since the rise of liberal judicial activism and the beginning of the conservative movement. They can tell themselves that this defeat will not be as lasting and deep as it otherwise seems it will be, because one day they will erase it all.
It also tacitly assumes that conservatives will not win any landslides of their own in the future. If conservatives do find themselves in the position to pack the courts after liberals have already legitimated the idea, then surely they will do so — it would be crazy for them not to do so.
And if each side treats the courts this way, then the courts will lose power relative to the elected branches. The growth in the political importance of the federal courts would have finally led to a correction in which the political branches re-asserted themselves, albeit rather bluntly. The rise of judicial power over the last 60 years has mostly benefited progressive causes; is the Left sure it wants to undo it?