He said the online debate had “crossed a line”, resulting in threats against MPs, including Safeguarding Minister Jess Phillips.
Sir Keir went on to accuse the Tories of “jumping on a bandwagon” to gain attention.
Conservative MPs were “amplifying what the far-right is saying” on child sexual abuse after failing to act “for 14 long years”, he added.
Describing child sexual exploitation as “utterly sickening”, Sir Keir defended his record in office as DPP – saying he tackled the issue “head on”.
While DPP, Sir Keir introduced a special prosecutor for child abuse and sexual exploitation to oversee convictions against grooming gangs.
He also changed the Crown Prosecution Service (CPS) guidance to encourage police to investigate suspects in complex sexual abuse cases and court reforms aimed at making the process less traumatic for victims.
“I changed the system because I could see some of the things that were going wrong,” he told reporters.
Sir Keir said he reopened cases, brought the first prosecution of an “Asian grooming gang” in Rochdale and called for mandatory reporting of child sexual abuse.
“When I left office, we had the highest number of child sexual abuse cases being prosecuted on record”, Sir Keir said.
“The victims here suffered terrible abuse,” he sid, “and then they weren’t listened to.”
Phillips had also “done a thousand times more” to protect victims of child sexual abuse than those attacking her can “even dreamt about”, he said.
