How about this

What would it look like if every person on the planet had basic access to a reasonable standard of food, housing, education and healthcare, and we all lived within sustainable environmental means?

I'd say it would look like less than two billion people, first off.

Aside from the fact we basically have no idea how to live environmentally sustainably with anything approaching a modern lifestyle, how do we feed people without fertilisers dependent on fossil fuel?

And if you can solve that, there are probably at least a dozen major problems we've barely started on, like for instance replacing thousands of plastics with a handful of properly recyclable ones, which simply won't even be addressed under capitalism, beyond the usual empty lip-service.

The first problem (aside from the population elephant in the room) is our means (or lack) of organisation. Nothing worth a damn will be sorted before that changes.

How can we viably continue without switching to a bottom-up system which actually tries to maximise our collective potential, rather than the epic waste of this pathetic divide and conquer shitshow?