It ruins the narrative of the attack being exploited to suit the government.
It is being used as an excuse to prevent marches and impede civil liberties.
This individual was known to Prevent. He was mentally ill. This is a failure of police and policy, and they want to capitalise on it to further their own aims.
If action had been taken when a mentally ill man stabbed a roommate, would he have been able to carry out subsequent racist assaults?
What is needed now is more police available to respond, making people feel safe to go to school and synagogue. Not a massive campaign of legislation to further the government's own ends.