Yes, it would be correct to say that socialism would be a lot easier to implement and operate with less people to provide for. But if wishes were horses, all beggars would ride, as the old saying goes. Socialism will inherit the problems capitalism has created for itself.
The reality is that globally the population is growing and the question is, can it be reduced? The stark answer is not immediately - even if fertility rates were lowered. The number of people in a country continues to rise for years after people stop having children-- a phenomenon known as population momentum.
Thus, the projection is that global population will go from approaching 8 billion today to about 11 billion in around year 2100 then plateauing and then finally begin to drop back to about what it is today. But even now such high figures are being challenged by experts in the field who suggest lower numbers and a an earlier date for the decline to commence
So socialists fully expect and are required to plan for an increased number of people, something that we cannot avoid regardless of any family planning which is already being increasingly adopted without any compulsion by better educated and more empowered women, even in patriarchal dominated cultures.
Our argument is that with rational allocation of resources that should not be a problem and free access can still be accomplished. We do have the capability of comfortably coping and still create a sustainable steady-state, zero-growth economy eventually.
This is not to say that population numbers and density will not be a critical crisis for capitalism and another reason why for the sake of humanity it must be done away with.
Along with a population rise we also have the related issues that will arise in the future.
Firstly, the demographic problem of higher numbers of elderly with less adults of working-age to support them. China's one-child policy resulted in what was called the 1 - 2 - 4 paradox. One active worker supporting retired parents and because of better health prospects his or her grand-parents. Such family support is essential in countries lacking social safety-nets for the old and frail.
Secondly, we also have the situation of urbanisation and over-crowding in slums and shanty towns of some major cities as the industrialised plantation-type cash-crop farming leads to the demise of the small-farmers. (To be exacerbated by climate change in many areas of the world)
And thirdly, we have the nationalist prejudice against the movement and migration of people. We witness this right now. The youth of Africa thwarted by lack of prospects seek opportunities in Europe where there is already a declining work-force that requires an influx of newcomers. But rather than be welcomed, they are being excluded.
Socialists cannot deny these conditions result in suffering and misery for as long as we live under capitalism. But we challenge the view that solutions cannot be achieved with the establishment of a cooperative society. In fact, only socialism can overcome them.
And that is the reason why great changes in people attitudes on how we view our world are required.