Although we are Humanists that doesn't mean we want a planet over-run with Humans! The Optimum Population Trust is in the news since David Attenborough has become one of its patrons. He says: "I’ve never seen a problem that wouldn’t be easier to solve with fewer people, or harder, and ultimately impossible, with more."
The Population Problem tends to be a taboo subject, because of the fear that it could only be controlled by coercive measures. But without some rational approach, presumably based on education and voluntary self-control, it is probable that population will be controlled in the end by flood, famine, pestilence and war.
The world population is now approaching 7 billion (that's 7 with nine zeros) and is projected to go over 9 billion by 2050. It is probably already well above the optimum at which pollution and damage to the environment can be avoided.