We need both, to reduce the total number of people AND to reduce the per capita consumption.

I have seen more than enough people that claim to have no children for the sake of the Environment, only to go and buy pets and treat those like children; retarded children that will never learn to speak, walk in 2 feet, or become productive members of society, demanding constant attention for their natural lifespan, and which will age rapidly and die in their teens, - and have valuable medical resources expended in heroic efforts to futily prolongue their agony for weeks/months. You could claim that the pet dies early and does not produce offspring, but then the pet owner will likely mourn for a few weeks and then go to the pet store and start all over again.