What I believe he means is that vaccines, healthcare etc. will cut child mortality in Africa (where the Gates Foundation has pumped lots of money for such programs) and elsewhere in the 3rd world. The operative assumption that follows is that the birthrate will plummet, reducing future population increases. It is amongst the poor populations of the world that population is increasing. Rising standards of living and the expectation that children will live to adulthood served to dramatically reduce birthrates throughout the 1st world. He is not looking to kill people, just slow the current rate of increase. If the birthrates throughout the world equaled that of Europeans, Japanese, Americans, Canadians and so forth, population would slowly begin to fall. The population of the US/Canada/Europe/Japan/Australia would already be declining if it weren’t for immigration from 3rd world countries.