I usually say if every human being on the planet were placed in Texas, it would be less dense than Paris as an argument against an area being "too crowded", but this is an even more jarring comparison.
And of course, crowded is relative. What I mean is that there is enough room and resources for everyone to live a comfortable and rich life. But it will look quite different from what people are striving for today. You can't eat beef every day, you can't live in a mansion, your family can't drive 2 big SUVs for daily transport, et c...
By eating less beef? The people hardly using resources aren't eating much of that anyway.
By biodiversity loss? We'd do a better job with that if we stop looking at in terms of effect on people and start caring about wildlife for its own sake, and that's the perspective I take when I say the planet is crowded: not just crowded for people, but people overcrowding the rest of nature.
But if you insist on focusing on people, we're all going to regret the loss of fish from the oceans.
Side note: I'm not sure who you meant but in some of those third-world countries that "hardly use resources," there are people doing major damage to biodiversity by burning down rainforests and hunting endangered animals. Their countries just aren't burning much fossil fuel.
can we thus rather go for grazing hoomans.