We have to remember that the Left (wherever it is) regards existing societies as an evil to demolished in order to make way for their perfect fantasy collective. Anyone, or any group, that acts in defense of the existing society is evil in the eyes of the Left.
Which is of course why the Left passionately hates the Police and the Armed Forces, both of whom have traditionally stood in the path of Holy Marxist Revolution and thus the establishment of the Holy Communist Society where all activities and relationships are dictated by the self-appointed revolutionary saviors and enforced by the compulsary power of the state.
The obvious corrolary is the Left appears to have a passionate love for the destroyers of civil society such as violent criminals and organized terrorists. They appear to especially found of those who murder police officers, such as Fidel Castro and Whatever Whatever Mumia. (No, I won't bother to look up the correct spelling.)
For a Leftist government (pardon the contradiction) to authorize the use of deadly force against any group of rioters would constitute a betrayal of its fundamental political premise, that civil society -- where economic and social relationships are based on consent -- is fit only for destruction.