Sir Mark said the author of the post could have “direct experience from the scene” but suspected “the more likely scenario is that they [were] another armchair critic”.
“Those officers are nothing short of extraordinary,” he wrote. “They were on the scene within a few minutes, and their actions undoubtedly prevented further injury and saved lives.”
Sir Mark said that “apprehending violent and dangerous criminals is a full contact and messy task which may appear shocking to observers with little experience of policing in the real world”.
“Officers need to know that when they act to protect Londoners decisively, they will be supported.”
He continued that, against the current backdrop, the right approach was not to inflame tensions further by “amplifying more ‘us and them rhetoric'”.
Liberal Democrat spokesperson Luke Taylor MP also criticised Polanski, describing his decision to repost the comment as “utterly disgraceful”.
“That ludicrous response and his comments on ‘perception of fear’ in the Jewish community tells us a lot about the Green Party’s values,” he said.
Essa Suleiman, 45, remains in police custody having been arrested on the suspicion of attempting to murder Shloime Rand, 34, and Moshe Shine, 76, in Golders Green on Wednesday morning.
Sir Mark said later the same day that the suspect had a history of serious violence and mental health issues, and was believed to be involved in a separate incident in south-east London on Tuesday.
The Met declared formally declared the attack a terrorist incident.
Polanski described the attack at the time as “horrendous” and said he was “thinking of the victims, their families and everyone who will once again be shaken by this attack”.