I think that your reasoning is a corruption of proof by induction, alternatively know as the continuum fallacy, the slippery slope argument, the 'How many hairs make a beard?' argument, the 'straw that broke the camel's back' argument etc.
The logical error results from concerning yourself with the difference between similar quantities rather than the effect of the whole. To give an example of how the fallacy works, you could argue that $999,999.99 is essentially the same as $1,000,000. Similarly, you could argue that $999,999.98 is essentially the same as $999,999.99. You could continue this argument down to $1 and argue that because the values are all essentially the same, $1,000,000 and $1 are the same. Clearly they are not the same.
In contrast to this, the argument that a larger number of people will have a larger environmental impact is sound imo. The critical question is 'At what level of population does the supporting environment start to break down for any given level of consumption?'.
My preference is to use the 'boiling frog' analogy for this argument. If you put a frog in water and raise the temperature slowly enough, the frog will be unaware of any temperature change. At some point though, the frog will start to cook and die, unaware of its fate to the end.
The latest Four Corners gives an excellent description of how this works, by contrasting the Gold Coast, Tweed and Byron Shires. You start off with a beautiful place like the Tweed Shire and by degrees turn it into a monstrosity like the Gold Coast, all along telling the residents that each change is only very small, but essential for their kids' future. The Gold Coast now has very high unemployment, a huge drug problem, and a level of crime that is not effectively policed. Meanwhile in the Tweed Shire, rising property values are now forcing residents, many elderly, from their homes. Interestingly, no mention of an increasing population as the cause was made.
The Gold Coast Shire also provides an example of a green 'drought'. Having taken a drive around the shire recently, I noticed many full dams and green fields and well fed stock. However, at the beach, I found that the showers had all been turned off because of the 'drought'. And all the grass that I saw there was green! There would be no such 'drought' with a lower population. You can download a graph of dam level and rainfall vs time for the Hinze Dam from
http://www.goldcoastwater.qld.gov.au/
On of the fixes for the 'drought' is the construction of a 120 MAUD pipeline from the Wivenhoe Dam. If the population keeps increasing there will no doubt be more 'droughts'. Then what? Another pipeline perhaps? A limit will be reached eventually. It is easy to think like copydog and believe that a city like Las Vegas is evidence that the desert can miraculously support a bustling metropolis of a few million citizens. But the resources have to come from somewhere, and plently of them.
The impact of an increasing population is slow but cumulative. It has observable effects, such as traffic congestion, destruction of native bushland, social displacement, increased water charges and restrictions, and recreational fishing bag limits. Unfortunately, what should have been a question of how best to preserve living standards and the environment was hijacked by the divisive One Nation, and like them it has fallen by the wayside.
But ask yourself 'Does population growth currently provide a net benefit to our citizens and the environment?'. Clearly it is benefiting some and harming others.
