I'm glad I'm living now and not in 100 years time.

That's part of the difference, perhaps. I expect still to be living at least 74 years from now, and maybe well beyond that.

Setting population limits is not necessary. As soon as women have the opportunity of birth control, they will use it (statistically). All you need to do is give them opportunity.

As you say, the global footprint has many conditions that are not fixed. We can also improve carrying capacity (see: Terra preta)

Now you have defined three variables (pollution is a fourth, but let's leave that out). The outcome you'd derive from these variables depends upon their relative size. Now we know the population variable to a fairly high degree and population looks set to peak at 8 billion around mid-century. Possibly less if Clinton/Obama/Edwards/whoever will undo the Bush line of not supporting birth control as a part of development aid.

So the population increase is not that big, relatively speaking. Economic growth also does not need to be big in material terms to give everyone an acceptable level of wealth. Some say we already have enough.

On the other hand, we have a huge level of waste. If we turn this waste into food - go full cycle - we'll have (temporarily) solved most problems.

Part of the mind-blowing-ness of the global footprint idea at first encounter might be that it is an aggregate measure. At the global level we have to look at the disaggregated picture. What holds for one resource may hold to a different degree for another resource, etc.