Do you realize this argument works for any X and X+k ? I assume you are not thinking that an infinite number of people would get along just fine, so clearly there are some other constraints. It may well be that those constraint kick in at a higher number than many assume, but it might as well be smaller.
> and we have never had so few cases of starvation as in modern times.
Hunger kills more people than Malaria, HIV / AIDS and tuberculosis combined.
About 925 million people are hungry (that's very roughly 1 in 7 people).
Undernutrition kills 5 million children under the age of 5 each year.
And all that's on the decline.
Yeah, while we should check the numbers, I am pretty sure there were far more poor and starving people 100 years ago, not in total number of course, but in proportion of the actual world population. When is the last time you heard about starvation in China, for example ?
10 billions won't be more of an issue that jumping from 1 to 3 was. It's actually a smaller increment vs where we are right now.