Some people posted messages on social media paying tribute to the assailant, and others placed flowers at the site of the attack outside the Sogo department store to commemorate him, after the attack on the night of July 1.
Speaking ahead of the weekly Executive Council meeting, Lam said such actions could incite others to commit similar violent offences.
“One has to ask yourself whether it fulfils the moral standard for somebody to mourn a person who deliberately attacked and wanted to kill a policeman on duty. I think that’s very obvious,” she said.
“If that is immoral, certainly I would want to see Hong Kong people refraining from conducting that sort of immoral acts which might intentionally or unintentionally have the undesirable impact of inciting more people to do that sort of acts or behaviours.”
The CE said there is a common fallacy that violence can be justified when there are problems in society.
“We should not, and need not, link the government’s performance to national security and public safety issues,” she said.
“The government is responsible for solving different problems in society such as the shortage of flats and poverty. But it’s a fallacy to say people can resort to violence or break the law because these problems exist.”
She added that the government will speed up its study on how the city’s laws can be improved to safeguard national security and public order.
Lam said she had asked all government departments and public bodies to work to prevent lawbreakers from “penetrating” education, broadcasting and the arts, and glorifying violence.