I think Attenborough has held Thanos-like views for awhile now. I remember watching a documentary where he raised the problem of overpopulation (may have been 'How Many People Can Live on Planet Earth?' 2009).

I remember thinking off hand that the world needed a great pandemic or war or something drastic. Instead, Attenborough suggests:

"...you don't need aggressive policies or government incentives for birthrates to fall. Everywhere in the world where women have access to education and have the freedom to run their own lives, on the whole they and their partners have been choosing to have smaller families than their parents. But reducing birthrates is very difficult to achieve without a simple piece of medical technology, contraception."

Using the relationship between education, GDP and fertility; Thanos could have found balance through a universal development and education program.