That's true, but perhaps the emissions can be mitigated in a targeted way beyond just reducing demand.
At the current rate of 1.2% that's only ~18 years.
Given that emission controls are a whole lot easier to implement than eliminating a huge portion of the world's population, I'd say it's a more realistic goal to pursue.
But I do suggest people advocating it join the front of the queue.
You'd need a 33% growth in population to offset a 25% reduction in pollution, 100% growth to offset a 50% reduction, and so on.