At its core, Leftism is the idea that the wealth of the society must be collectivised, using force if necessary. That is, those who have more must be forced to share their wealth with those who have less. In reality the collectivisation doesn’t help the poor or Middle Class, neither immediately, nor in the long run. Immediately it kills and impoverishes the rich, and in the long run it kills millions of all classes, and impoverishes everybody.
By the way, collectivisation goes by many names (The names change every few decades because the Leftists, as they start afresh on the same folly, do not want anybody to know that they are doing the same thing again)- communism, socialism, Progressivism, Welfare State, Positive Rights to Free stuff (RTE, FSB, MGNREGA, Obamacare, etc.), and so on.
Collectivisation appeals to people, even to many rich, because it appeals to our instincts. The instincts from the early stages of our evolution when we used to be in small bands, with same purpose of hunting and gathering the food, and sharing it with all the members of the small band. But Civilisation was made possible, and is about, growing out of those small groups, and striking out on our own, individually. This was made possible by the custom of respecting private property of the individuals. (Without the custom of the respect for private property, private property could not have existed.) Private property led to individuals entering into contracts to exchange it, and with the contracts was born trade. And with the trade was born the Civilisation. Civilisation that has made possible explosion in human population and enabled man to populate all parts of the earth, and beat every other species.
Civilisation is basically the result of man’s control on his instincts, and his respect for the customs and morals. And no, it is not the result of our reason. Because customs and morals lie between our instincts and our reason.
Leftists are not able to cope with the demands of the Civilisation, which demands that every human being learn some skill which his fellow human beings are ready to pay for. They want us to take back to those small groups when all that was needed was to go out in the morning to hunt and gather, and the day’s collection was shared equally in the group. But if we agree with them, we would lose the Civilisation, and with modern Civilisation not to support, millions will die, and the rest would go back to primitive living. Leftists want us to go back to our instincts of group solidarity and altruism. Without ever realising the consequences of their quest.