One of the principal aims of the left has always been to destroy the true source of morality which is religion. It has done this because the powers behind the left want to remake humanity in a form severed from the supernatural. In this way, the possibility of spiritual redemption is removed and we become easy victims of these powers. We hand our souls over to them, convinced that this is the path of righteousness even though, on some level, there is an awareness that we are submitting to evil. But, if it suits the desires of our self-centred egos and validates our resentments, we can justify any action and paint vice as virtue.
Clearly, from a normal perspective this theory sounds absurd but let us assume that God is actually real. In that case, does it not explain the developments of the last 300 years rather well? For in that time we have descended more and more deeply into materialism and every time a frontier is crossed, the next one is set up a little further down the road. The spiritual descent is disguised by the fact of a sometimes real, sometimes just perceived improvement in other areas, material, social or whatever, but spiritual descent there is and continues to be. What does it benefit a man if he gains the whole world but loses his soul in the process? Yet this is the path we are set upon and have been for some time now.
The true source of morality has been destroyed but because human beings are moral beings (in that, however much they may deny it to themselves, they are spiritual beings), the left must invent a morality of its own. This morality is born of an ideology which then assumes the trappings of a religion, even though it can save no one and explain nothing, and that is why leftists can become so passionate about their beliefs. These have become their equivalent of religion, a false religion to be sure because it is not grounded in transcendent reality (indeed, it specifically rejects that), but a deformed kind of religion all the same.
If our morality becomes one of the principal ways by which we define ourselves, then the left has identified itself with a lie. Now, this requires an active choice, and it is a choice based on an inner orientation of character. This is an important point which should not be forgotten. Our beliefs reflect who we are. Broadly speaking, in life human beings are presented with two ways which are the way of spirit and the way of matter. They are not mutually exclusive but it is a question of which predominates. The transcendent-rejecting left has chosen the way of matter which is the false way, and it has chosen the false way because something in it is false. I might be accused of painting the picture in very black and white terms here and reminded that things are never that simple. But if you go down to basics and examine the human heart when it is faced with fundamental choices and decisions, I would suggest things are simple. The choice you make is who you are. It is determined by whether you respond more to truth, even if that requires sacrifice, or a lie which may in some sense strengthen and comfort your ego using that word to mean the separate self seeking its own validation.
I am not saying leftists are evil in themselves. But, to a greater or lesser extent, they have allowed themselves to follow a lie. Some may have done so out of naivety or because leftism is currently presented as the good and intelligent person's natural political home. But, whatever the reason, it means that the truth is not in them. In some there is actual darkness and in others just an absence of light, but in none is there light. Nevertheless, the potential for light exists in us all. We have only to turn towards it in humility and it will be there.
Note: Shortly after I wrote this piece I noticed Bruce Charlton has done a post on a similar subject though Bruce goes into the mechanisms behind the Leftist attitude more deeply than I have done. A happy coincidence! See here http://charltonteaching.blogspot.com/2019/02/leftist-motivation-how-resentment-and.html