You keep confusing the far left with liberals. The American "far left" is practically non-existent. Actual Marxists, and communists, are extremely tough on crime. These wet-bread, limp-wristed liberals aren't true "leftists", much less "far leftists", they're in a category of their own.
Modern American "progressivist" liberalism is a unique phenomenon, that is extremely nihilistic and unscientific. They hate science, reality, and authority. Actual Marxists recognize the value and importance of authority, social order, and security. Mobs of unruly, violent youth would be rounded up and detained, then placed in re-education work camps until they prove they can be law-abiding citizens. Their parents i.e. legal guardians would also be punished and forced to be re-educated in how to raise good citizens (members of society).