Salman Rushdie has warned young people against forgetting the value of free speech and discussed the “very big and negative” impact of a second Trump presidency in a rare public appearance since his stabbing.

The Indian-born British-American author of books including the Satanic Verses and Midnight’s Children also discussed the attack in 2022 that left him blind in one eye during a Q&A at an English PEN event at the Southbank Centre.

“I have a very old-fashioned view about [free speech],” said Rushdie, appearing by video from his home in New York to mark the launch of his new memoir, Knife: Meditations After an Attempted Murder. “The defence of free expression begins at the point at which somebody says something you don’t like.

“It’s a very simple thing, but it’s being forgotten. That is what’s enshrined in the first amendment … In the US, you feel there’s a younger generation that’s kind of forgetting the value of that. Often, for reasons they would believe to be virtuous, they’re prepared to suppress kinds of speech with which they don’t sympathise. It’s a slippery slope. And look out, because the person slipping down that slope could be you.”

Rushdie said academia in America was “in serious trouble … because of colossal political divisions. And everybody is so angry that it seems very difficult to find a common place.”

The Booker-prize-winning author, whose books have been translated into more than 40 languages, discussed the prospect of a second Trump presidency with the author and critic Erica Wagner and encouraged young people in the US to “not make the mistake of not voting”.

He said: “The impact would be very big and negative. He’d be worse a second time around, because he’d be unleashed and vengeful. All he talks about is revenge. And that’s a bad policy platform, that you want to be president to deal revenge against your enemies.

“In New York, people had got the point of Donald Trump long before he ever tried to run for office. Everybody knew that he was a buffoon and a liar. And unfortunately, America had to find out the hard way. I just hope they don’t fall for it again.”

Rushdie was about to give a talk at the Chautauqua Institution in New York state on 12 August 2022 when a man rushed on stage and stabbed him about 10 times. “I saw the man in black running toward me down the right-hand side of the seating area,” he recalls in his new book. The writer was hospitalised for six weeks.

On Sunday, he said he hadn’t been able to think about writing for six months, but then it struck him that it would be “ludicrous” to write about anything else.

He described the difficulty of penning the first chapter, “in which I have to describe in some detail the exact nature of the attack. It was very hard to do.”

Knife, the writer said, was the “only book I’ve ever written with the help of a therapist. It gave me back control of the narrative. Instead of being a man lying on the stage with a pool of blood, I’m a man writing a book about a man live on stage with a pool of blood. That felt good.”

Rushdie also spoke about the postponement of the trial of his attacker, Hadi Matar. He said Matar’s not-guilty plea was “an absurdity” and that he would testify at any future trial. “It doesn’t bother me to be in the courtroom with him. It should bother him.”

In Knife, Matar is not named, but referred to as “the A”. Rushdie said he was inspired by a Margaret Thatcher line about “wanting to deny the terrorists what she called the oxygen of publicity. That phrase stuck in my head. I thought, ‘This guy had his 27 seconds of fame. And now he should go back to being nobody.’

“I use this initial A because I thought there were many things he was: a would-be assassin, an assailant, an adversary … an ass.”

However, Rushdie said, “the most interesting” part of the book to write was the 30 pages of imagined dialogue between him and his attacker.

“I actually wanted to meet him and ask him some questions. Then I read about this incident where Samuel Beckett was the victim of a knife attack in Paris by a pimp. He went to the man’s trial, and at the end of it said to him: ‘Why did you do it?’ And the only thing the man said was: ‘I don’t know, I’m sorry.’ I thought: if I actually were to meet this guy, I would get some banality.”

So Rushdie decided it would “be better to try to imagine myself” into the head of a person who chose to attack a stranger despite reading “no more than two pages of something I’d written”.

‘There is in my mind an absence in his story,” he said. “This is somebody who was 24 years old. He must have known that he was going to be wrecking his life as well as mine, and yet he was willing to commit murder. He’s somebody with no previous criminal record and not on any kind of terrorism watch list. Just a kid in Fairview, New Jersey. And to go from that to murder is a very big jump.”