Well, it doesn't get much more alarmist than this.
Knight writes, "Fifty years ago, I concluded that the best thing for the planet would be a peaceful phase-out of human existence. We're causing the extinction of hundreds of thousands of other species. With us gone, I believe ecosystems will be restored and there will be enough of everything. No more fighting over resources."
Knight also pointed out that he himself took steps to further this idea by voluntarily getting sterilized in the 1970s.
All things considered, maybe it's a good idea he did that.