On average, people produce more than they consume.
But we don't produce more than we consume of some resources that seem important to our modern way of life (water, oil, etc). And off the top of my head I can't think of any good reason why having more people would bring us closer to making things like fusion a reality (other than by increasing the need).
Well, we won't need fusion for some time; at current wealth-creation rates, fission and solar can keep us well-supplied for a century or more, even without off-planet resources, which are fairly easily available. Water for human needs is not actually very scarce; it's just slightly more expensive than we'd prefer in some locations. Even current oil prices are speeding development of alternatives, and there is a lot of shale oil to help us transition from cheap oil to cheap solar or cheap fission. France has gotten most of its electricity from nuclear fission for decades, and exports power, so it's no longer a question of feasibility -- we know exactly how to solve our energy needs for several (current) lifetimes, and it will cost about what the Iraq war already cost to switch.
Basically, there are no particular shortages of anything that will necessarily be critical; the main thing we need to do to get over the hill we can see coming up is to stop braking so hard on the downslope of this hill. :)
But we don't produce more than we consume of some resources that seem important to our modern way of life (water, oil, etc). And off the top of my head I can't think of any good reason why having more people would bring us closer to making things like fusion a reality (other than by increasing the need).