The US supreme court could “at some point” become “compromised” by politics, said Clarence Thomas – one of six conservatives on the nine-member court after Republicans denied Barack Obama a nomination then rammed three new justices through during the hard-right presidency of Donald Trump.

“You can cavalierly talk about packing or stacking the court,” said Thomas, whose wife, Ginni Thomas, has come under extensive scrutiny for work for rightwing groups including supporting Trump’s attempts to overturn an election.

“You can cavalierly talk about doing this or doing that. At some point the institution is going to be compromised.”

Thomas was speaking at a hotel in Salt Lake City on Friday.

“By doing this,” he said, “you continue to chip away at the respect of the institutions that the next generation is going to need if they’re going to have civil society.”

The court is set to rule this year on divisive issues including abortion, gun control, the climate crisis and voting rights. Conservative victories are expected. The conservative-dominated court has already ruled against the Biden administration on coronavirus mitigation and other matters.

The US constitution does not mandate that the court consist of nine justices. Some progressives and Democratic politicians have therefore called to expand it, in order to reset its ideological balance. Democrats in Congress last year introduced a bill to add four justices and Joe Biden has created a commission to study expansion.

Few analysts think expansion is likely to happen.

Republican senators are currently attacking Biden for his campaign promise to nominate a first Black woman to the court, a promise he fulfilled by nominating Ketanji Brown Jackson to replace the retiring Stephen Breyer.

Republican presidents have nominated justices on grounds of identity, most recently when Trump said he would pick a woman to replace Ruth Bader Ginsberg, the liberal lion who died in September 2020.

Ignoring their own claims about the impropriety of confirmations in election years, made in denying Merrick Garland even a hearing to replace Antonin Scalia in 2016, Senate Republicans installed Amy Coney Barrett, a hardline Catholic conservative, as Ginsberg’s replacement.

In Utah on Friday, Thomas also voiced a familiar conservative complaint about so-called “cancel culture”, the supposed silencing of voices or world views deemed unacceptable on political grounds.

He was, he said, “afraid, particularly in this world of cancel culture attack, I don’t know where you’re going to learn to engage as we did when I grew up.

“If you don’t learn at that level in high school, in grammar school, in your neighborhood, or in civic organizations, then how do you have it when you’re making decisions in government, in the legislature, or in the courts?”

Thomas also attacked the media for, he said, cultivating inaccurate impressions about public figures including himself, his wife and Scalia.

Ginni Thomas has faced scrutiny for her involvement in groups that file briefs about cases in front of the supreme court, as well as using Facebook to amplify partisan attacks.

Thomas has claimed the supreme court is above politics – a claim made by justices on either side of the partisan divide.

Congress is preparing for confirmation hearings for Jackson. She will be installed if all 50 Democratic senators back her, via the casting vote of the vice-president, Kamala Harris. Some Republicans have indicated they could support her too.

In Utah, Thomas recalled his own confirmation in 1991 as a humiliating and embarrassing experience. Lawmakers including Biden grilled Thomas about sexual harassment allegations from Anita Hill, a former employee, leading him to call the experience a “high tech lynching”. Biden has also been criticised for his treatment of Hill.

On Friday, Thomas said he held civility as one of his highest values. He said he learned to respect institutions and debate civilly with those who disagreed with him during his years in school.

Based on conversations with students in recent years, he said, he does not believe colleges are now welcoming places for productive debate, particularly for students who support what he described as traditional families or oppose abortion.

Thomas did not reference the future of Roe v Wade, the 1973 decision that guaranteed abortion rights. The court on which he sits is scheduled to rule this year on Dobbs v Jackson Women’s Health Organization, concerning whether Mississippi can ban abortions at 15 weeks.

The court is expected to overturn Roe. While the justices deliberate, conservative lawmakers in Florida, West Virginia and Kentucky are advancing similar legislation.

• The Associated Press contributed to this report