If I could wax philosophical about this for a moment...
I've encountered extreme Left philosophies in action in Africa, Europe and South America, as well as here in the USA, and I think I can speak with some depth of knowledge and experience about them.
To me the deepest root of the problem is very simply defined. The Left will work for, or against, an idea and/or a thing, but not a person. They have a fundamental blind spot about the value of the individual. Their hysterical cries about "human rights" and "it's for the children!!!" are actually inhuman in the effects they have on individuals. They regard society - the broad mass of the people - as fundamentally more important than each individual member who makes up that society. This is why they so often try to take over, or alternatively divorce themselves from, faith-based communities: every major deistic faith emphasizes that the individual is important, that individual decisions and actions count.
This is illustrated very clearly in the RKBA battle. The Left decries the thing - the gun - and ignores the person wielding it. The Left also ignores the effects of disarming the righteous - they're satisfied that the "evil thing" has been removed, and ignore the effect on now-defenceless individuals.
Of course, many right-wing movements have precisely the same problem. They try to mobilize people into a mass movement, just as does the Left. This is why, IMHO, the dimension of religion and spirituality is so vitally important - it's often the only area of society that consistently practices, and preaches, individual responsibility (which, of course, translates into individual rights of the proper kind - taking responsibility for exercising a right, rather than demanding to be able to exercise the right without the corresponding duties and responsibilities). I know there are many who will disagree with me on the importance of the religious dimension, but there we are...