The chief justice of New South Wales has criticised former prime minister Tony Abbott for what he says was a regrettable, misconceived and ignorant attack on a judge’s decision regarding last year’s pro-Palestine Sydney Harbour Bridge march.

Andrew Bell said in a speech on Thursday evening that Abbott’s post on X in August last year threatened social cohesion.

Abbott commented on a NSW supreme court decision before the Gaza harbour bridge march that an estimated 225,000 to 300,000 people attended.

The former Liberal leader posted that “it should not be for judges to decide when a political protest is justified”.

“The decision to close the Sydney Harbour Bridge to facilitate this protest is a political decision and should be made by elected and accountable ministers – who, it happens, think the march should not go ahead,” Abbott wrote at the time.

“We are on a slippery slope when unelected judges start making political judgments.”

Bell, in a speech at a dinner to mark the opening of the law term, said on Thursday that Abbott had “regrettably” posted about justice Belinda Rigg’s decision. He said the comment on X was “misconceived”.

“The judge’s decision was not one concerning whether ‘a political protest was justified as any understanding of the statutory framework and case law set out in the judge’s reasons would have made plain to anyone who took the time to read it,” the chief justice told diners.

“The judge did not make ‘the decision to close the Sydney Harbour Bridge’. The authorities had already taken the decision to close the harbour bridge in any event, that is to say, irrespective of the judge’s decision, a fact twice recorded in the judgment and one which was influential in the ultimate decision.

“Responsibility for the decision the subject of the criticism was one expressly given to the court by the legislature; it was not an unauthorised assumption of jurisdiction by ‘an unelected judge’.”

Bell concluded that Rigg’s decision “was not a ‘political’ judgment but involved the careful weighing of the common law and constitutionally protected right to free speech and public assembly”.

He added that a subsequent court of appeal decision over which he presided, which prevented a march to the Opera House, was also not a “political decision” but involved a similar weighing exercise.

Bell, earlier in Thursday’s speech, criticised other “simplistic but frequently highly personal criticism” in the press and on social media of some judges who had granted bail where the prisoner had subsequently reoffended.

“While judicial decisions on subjects such as bail and public assemblies should not be free from scrutiny or criticism where justified, social cohesion to which I have already referred is not enhanced when judicial decisions are attacked on bases and in terms that betray an ignorance of the statutory framework for the decision and, in very many cases, an ignorance of the judge’s reasoning process and of the evidence before the court by reference to which the decision was made,” Bell said.

“Such attacks, often dashed ‘off the cuff’, are a form of misinformation that undermines trust in and respect for the judiciary and the rule of law.”

The chief justice added: “I should note in this context that two judges of the supreme court, who have been the subject of highly personalised and misconceived criticism in some sections of the media for particular decisions, have received death threats in the last 18 months. This is obviously of grave concern.”

Abbott was contacted for comment.