I can psychologically understand the furious reaction "we sold our souls for this 6-3 Supreme Court majority and that means we have a right to have it securely delivered" but it doesn't inspire much sympathy.

Those who cheerfully endorsed or cynically tolerated the last 4 years of assault on the rule of law, the separation of powers, due process, and procedural norms all for the sake of judicial appointments might feel that the price they paid increases their claim on that 6th seat...

but it makes them singularly unpersuasive defenders of the norm against court expansion and its associated protection of judicial independence. This is the accused murderer of his parents throwing himself on the mercy of the court (so to speak) because he's an orphan.

That doesn't mean there's no grounds for worry about breaking this norm. But four years of the cynical anti-anti-Trump posture of the #ButGorsuch-ers makes it hard not to end up being anti-anti-court-packing. That seems to be where Biden is, or where he's on his way to.