I think you are in denial. This is coming from the left.
The left is allowing itself to be taken over by groups from the fringes with anti-progressive aims.
Something similar is happening to the right. However, no one would seriously argue that the right is being infiltrated by the left in a cunning plan to destroy them from the inside.
Both the left and the right are doing this to themselves. It's to do with the collapse of the centre.