It'd be really interesting to figure out what we actually
can all do, though, based on first principles and some basic math. Right now there's a lot of rhetoric on both sides, either of the form "The universe is scarce. Either we compete over natural resources, or we die" or "There's plenty for everybody! Let's guarantee everyone a middle-class American lifestyle as a basic human right." I suspect that both extremes are quite inaccurate, and being manipulated for political gain.
Two surprising ones that I've found:
We can feed everyone on earth. Current daily food production per capita exceeds the recommended 2500 Cal/day in all regions [1], even in Africa, and exceeds 3500 Cal/day in some regions (North America, Europe). With current technology, we could feed the expected 2050 population of 9B. We may not be able to feed them meat, because it takes roughly 25x as much energy to produce beef than corn, and roughly 6x as much for chicken or pork. [2] We also need to fix severe distribution and supply chain leakage problems to get the food to where it needs to be.
We also can produce enough renewable energy to give everyone a developed-world standard of living, subject to construction & storage costs. Energy use in the U.S. was 4.1 TWh in 2016 [3]; divided by 8760 hours/year, that's a mean power usage of 472.2 GW. (Peak power generating capacity in the U.S. is about 1100 GW, so that implies 50% utilization, which is about right.) Scaled up to 9B people (30x), that implies a global energy consumption of around 14 TW. Solar flux on the earth is 1.361 KW/m^2 [4], so at 10% efficiency, that requires an area of 104,010 square kilometers covered by solar panels. This sounds large, but laid out into a rectangle, it's only about 250 * 400 km. Such an array could easily fit into the Mojava, Sahara, or many other deserts on earth, with plenty of room left over.
We likely can't all live in the country - total habitable acreage on earth is about 15.77 billion acres, so with 9B people, each person gets about an acre and a half, and that has to include all the public commons, infrastructure, industry, etc. as well. We also probably can't all have a car - we could if we all lived in the country, but if you take say SF's density (20K/mi^2), give everyone a car, and multiply that by the space the car takes up in parking (say 200 ft^2) and roads (depends on density, but let's say equivalent), you're looking at 8M ft^2 taken up by vehicles alone out of a total available space of 27M ft^2. If everybody used motorcycles, pods, or scooters to get around, it could work, though.
[1] https://ourworldindata.org/food-per-person
[2] http://www.pnas.org/content/115/15/3804
[3] https://en.wikipedia.org/wiki/Energy_in_the_United_States#Co...
[4] https://en.wikipedia.org/wiki/Solar_constant