I suppose first we should consider food. For that we look at what every human needs to consume (considering all necessary vitamins and minerals in addition to obvious calories) and then try to figure out what sources of those nutrients is currently the most efficient at producing them. Then there should be data somewhere on how much of that foodstuff is produced per year and how many people are employed in producing it. If not enough of that foodstuff is produced to meet the planet's needs for that nutrient, then move on to the second-most efficient source and so on until the need is met. Then the same again for the next vital nutrient, hopefully with overlap on sources of previous nutrients. And so on until all nutrients are accounted for, and that should provide a number for how many people are directly involved in the production of the food. That would be the primary list. THEN we would need to consider secondary elements for food production: everyone involved in producing the tools/resources used in direct production (tractors, combine harvesters, fuel, fertilizer, etc), but ONLY calculating for JUST enough to meet the demand represented by the primary list. Surplus manufacturing to be ignored. Keep going that way until you have it all the way down to raw materials (steel, silicon, rubber, etc). Finally, you look at the distribution network necessary to actually get all of these things where they're needed. This would, naturally, include workers employed at road maintenance, transport drivers (although billionaires seem fairly insistent that these jobs can be eliminated soon), etc. That would provide you with the BARE MINIMUM workers necessary for food production.

Then you perform a similar process for the production of:

• Housing

• Clothing

• Healthcare

• Education

Once you have the bare minimum, you can actually talk in concrete terms of just how much of humanity is employed in essential work and how much isn't. Most likely, when evaluating clothing, the "most efficient source" was sweat shops, so once you know that humanity has enough non-essential workers, you can make a compelling case that laws need to be passed to guarantee that more workers are diverted to clothing production, with an aim of providing better working conditions for all.

We can't really have intelligent conversations about whether capitalism is or isn't a good way to allocate resources until we have the data on what the optiminal use would be. We all SAY that the world produces enough for everyone, but nobody really KNOWS.