Collectivism is core to leftist mindsets, at least of their shock troops. Their mental deficiency, being unable to recognize the existence of individuals from group behavior, is required to buy into the absolute bullshit they produce, and is deliberately built into them by media and propaganda in education.

Their rulers actually don't have this deficiency, they just use it to their benefit. Leftist ideologies like socialism are tools for sociopaths to use to gain power, that is their actual purpose.