Nor should a judge give the impression of being consumed by hatred for one of the main political parties.
Mr Kavanaugh described the allegations against him as "a political hit",
"revenge on behalf of the Clintons"
and the fruit of "millions of dollars in money from outside left-wing opposition groups".
Defenders of Mr Kavanaugh, worried about an open season on powerful men,
point out that any innocent person in his position would rage against his accusers.
Yet Mr Kavanaugh was not just angry, but conspiratorial.
He chose to direct his fury at the Democrats personally, as if he were a signed-up member of the other side.
As it happens, that is precisely what Democrats have always alleged—and how Republicans are now honouring him.
Before he became a judge, Mr Kavanaugh worked for Ken Starr on the impeachment of Bill Clinton.
He was part of George W. Bush’s legal team, which opposed a recount in Florida in 2000, and later worked in the Bush White House.
This explains why hostility to Mr Kavanaugh has eclipsed that faced by Neil Gorsuch, who joined the Supreme Court last year.
Mr Kavanaugh says he put party allegiance aside on becoming a judge.
After last week, that claim looks misleading, too.
It is hard to see how someone who harbours such feelings can decide cases on gerrymandering, say, in a credibly non-partisan way.
Mr Kavanaugh's conservative judicial philosophy is not a problem.
His visible loathing of Democrats is.
That is not just our opinion.
In 2015 a prominent jurist told the Catholic University of America: "A good judge, like a good umpire, cannot act as a partisan...
If you are playing the Yankees, you don't want the umpires to show up wearing pinstripes."
The jurist's name was Brett Kavanaugh.