“I think the media makes it sound as though you are just always going right to your personal preference,” Thomas said, at Notre Dame University in Indiana.
“So if they think you are anti-abortion or something personally, they think that’s the way you always will come out. They think you’re for this or for that. They think you become like a politician.
“That’s a problem. You’re going to jeopardise any faith in the legal institutions.”
Supporters of abortion rights fear the move previews a formal overturning of Roe v Wade, the 1973 ruling which guarantees the right, through a case from Mississippi.
“We’ve gotten to the point where we’re really good at finding something that separates us,” Thomas said.
He also said: “It’s not about winning and losing at the court.”
Thomas is only the latest justice to insist members of a court on which liberals are outnumbered 6-3 do not rule according to political beliefs.
Last week, the conservative Amy Coney Barrett said “judicial philosophies are not the same as political parties” and claimed the court was “not comprised of a bunch of partisan hacks”.
She was speaking at a Kentucky centre named for Mitch McConnell, the Republican Senate leader who defied convention to block Barack Obama’s third pick to the court, oversaw two picks by Donald Trump including the hugely controversial Brett Kavanaugh, then ripped up his own precedent to rush Barrett’s confirmation in place of a liberal lion, Ruth Bader Ginsburg, shortly before the last election.
At 83, the liberal justice Stephen Breyer is the oldest member of the court, a target of calls to retire from progressives who see a narrowing window for his replacement by a Democratic White House and Senate.
Breyer has said he does not intend to die on the court, as Ginsburg did, but has not indicated when he might step down.
He has also written a book, The Authority of the Court and the Peril of Politics. Last weekend he told Fox News Sunday: “I’m there for everybody. I’m not just there for the Democrats. I’m not just there for the Republicans. And I’m not just there because a president was a Democrat who appointed me.”
Joe Biden has promised to put a Black woman on the court. In Peril, a new book out next week, the Washington Post reporters Bob Woodward and Robert Costa detail how that promise, a political act in itself, was the result of an endorsement from the South Carolina congressman James Clyburn which did much to propel Biden through the Democratic primary and into the Oval Office.
Thomas, the only African American on the court, has been a consistent presence on the hard right since his highly contentious confirmation in 1991, when he was accused of sexual harassment by a former colleague. At Notre Dame, protesters shouted “I still believe Anita Hill” before being removed.
Thomas said he “almost never” changed his mind as a result of oral arguments. Infamous for rarely speaking during such proceedings, in 2016 he made headlines by breaking a 10-year silence to ask questions in defence of gun rights.
At Notre Dame, he said lawyers sometimes performed so badly justices’ minds were changed. He also said some rulings “conflict very strongly with my personal opinion, my policy preferences”.
Many on the left want Biden to expand the court to redress its ideological balance, thereby playing the sort of hardball politics Republicans have used without compunction. The constitution does not limit the number of justices on the court.
Thomas did not directly address the issue. But he did say the US “should be really, really careful” about “destroying our institutions”.
“The court was thought to be the least dangerous branch [of government] and we may have become the most dangerous,” he said.