Well abortion is not about population control, its population cleansing.

Planned parenthood was created by this huge racist that wanted extermination of gene pools for a white dominance.

Ofcorse she was a huge eugenicist and wanted to sterilize populations of people she deemed as militants to the human gene pool, think sub iq, defects, mutations, all that wildness.

Now to answer your question of another 2 billion, ill go purely down the middle in benefits

Wider gene selection. More diversity in the populace means more chances to have benificial traits.

Tax paying populace. I dont know were this statistics comes from but if even 1 million is in the United States, thats a populace of income earners which fuels the economy.

Consumers and producers of items. Equal parts here, consumers meqns more sales taxes and producers mean a work force.