The case for socialism — a society of common ownership, democratic control, production for use and distribution according to need — rests on the fact that capitalism does not work, and cannot be made to work, in the interests of the majority in society who have to go out to work for a wage or salary.
Capitalism is a class-divided society in which the means of production are owned and controlled by a minority of extremely rich individuals. Goods and services, useful things, are produced not with the intention of satisfying our needs, but with the intention of making a profit for this minority. Production is subject to the profit motive. The economic law of "no profit, no production" rules.
Basically, capitalism can only work as a profit-making system in the interests of those who live off profits. It is because priority must be given to making profits that the needs of the wage and salary working majority are neglected. Profits come first. People's needs come second.
This is why the majority face problems even when it comes to meeting our basic needs. This is why there are problems over the quality of the food we eat. Why there are millions of people living in substandard housing, and why some are completely homeless. Why the health service is run on the cheap. Why there are problems over schools, transport, the environment — in fact why there are all the problems which the politicians promise to solve but never do.
Capitalism is not just a national phenomenon. It exists in all countries including, obviously now, in Russia. It is in fact a world system, and the problems of world poverty, ignorance and disease are to be laid at its door too. The productive forces exist to provide every man, woman and child on this planet with adequate food, clothing and shelter. Yet millions die each year of starvation or starvation-related diseases, while farmers in Europe and North America are paid not to grow food. These people die because they have no money and so don't constitute a market. Which means they don't count for the operation of the capitalist system.
Because capitalism involves a built-in competitive struggle for profits there is also a struggle that from time to time breaks out into actual warfare for sources of raw materials, for markets, for investment outlets and for strategic points and routes to protect these. To be prepared for this, and as a "deterrent" to other states to keep their distance, all of the states into which the world is divided have to maintain the most destructive weapons of war they can afford. So the world spends more on armaments than on dealing with problems like starvation and disease. So, also, the major powers have stockpiled enough nuclear weapons to destroy humanity many times over.
As if the threat of nuclear annihilation was not enough, there is also the threat of ecological disaster — either from global warming or from the hole in the ozone layer, take your pick — caused by industrial processes firms are forced to adopt to remain competitive and stay in the race for profits. So this is capitalism. And this is why we must get rid of it.
We must replace capitalism with socialism. A complete change in the basis of society, from class ownership and production for profit to common ownership and production just for use, must be brought about by conscious democratic political action before anything lasting or constructive can be done to solve existing problems. With common ownership and democratic control we will be freed from the tyranny of the economic laws of capitalism which restrict and distort what is produced to what is profitable. The barrier to us using the means of production to meet our needs will have gone.