I'm just writing a blog post (it will be up soon ) on global population. Global population is declining (and declining quickly). A recent study concluded that human population should stabilize around 2050 between 8-9 billion individuals. Overpopulation is always what incredulous people say when futurists discuss the possibility of radical life extension. But those people don't realize that the largest demographic shift in human history is already underway and accelerating.

Also, if the technology to extend life indefinitely exists... people won't turn it down. Think about the technologies that exist today that enable more people than ever in the history of our species to live into their 80s and 90s. Do any of them say "no it would be selfish to get this heart transplant... just let me die." Hardly anyone. If we develop technologies that allow people to remain healthy and live much longer... no one will turn it down. The result of these transitions will be a human species that have very few children (if any) and live much longer (150-200) and those are conservative estimates.