Over-population is not the immediate problem facing the world. The problem is that class rule and the profit motive stand in the way of the intelligent, environmentally sound production and equitable distribution of the goods and services needed to satisfy human needs and wants.
In 2016 agriculture has brought bountiful harvests, and record surpluses of grain which are now out-supplying storage facilities. Yet millions of people, mostly children, die each year from hunger-related diseases, and 800 million more suffer the ravages of chronic malnutrition. Throughout the developing world transnational agri-capitalists, often in collaboration with local landowners, have dispossessed peasants from subsistence farming. They have turned much of the best land over to producing cash crops for export to foreign markets because profits are higher than in producing foodstuffs for local consumption. Compounding this, displaced peasants can't find jobs as wage workers. Millions starve, not because food isn't available, but because they don't have the money to buy it. To a lesser degree, the spectre of hunger also haunts exploited workers in the advanced capitalist countries, especially the growing numbers of permanently unemployed who have to resort to charity and food-banks. Starvation amid plenty strikes many people as an absurd paradox. However, under a system in which commodities -- including food -- are produced for sale with a view toward profit, it is perfectly logical. A socialist reconstruction of society is required to eliminate the cruel and preventable absurdity of people going hungry and starving in a world choking on "too much" grain. World hunger today is a product or the production of food as a commodity for sale with a view toward profit. Like the production of any other commodity, the production of food is governed basically by the narrow, antisocial decisions of the capitalist owners of industry, and by the constraints of market demand - which is determined by income, not human need.
Malthusian over-population theory cannot explain such facts. But socialists can. It is not population growth, but the profit-motivated capitalist system that causes the reckless squandering and waste of food and other natural resources as well. The production of weapons, for example, and maintenance of large military forces consume huge quantities of resources from iron ore to petroleum. In a sane society, those resources would be used to improve the quality of life. Capitalism is likewise characterized by the needless duplication of commodities and planned obsolescence. Similarly, the profit motive gives capitalists no incentive to curb the industrial pollution that is seriously damaging the environment or to rely on renewable sources of energy instead of finite supplies of fossil fuels, whose carbon emissions further pollutes the atmosphere.
This is not to say that it will never become necessary or desirable for society to set some limits on population growth. But, it should be noted, first, that population growth tends to slow down on its own as standards of living rise. In fact, in many advanced capitalist countries, populations are actually beginning to fall. A socialist society would likely extend the same trend worldwide.
"if at some stage communist [socialist] society finds itself obliged to regulate the production of human beings, just as it has already come to regulate the production of things, it will be precisely this society, and this society alone, which can carry this out without difficulty."
Only a society based on social and economic democracy can ensure that social policies will automatically be based on the social interest.