Less humans = more space and other resources for the other humans.
If many people die, I won't complain, I respect their sacrifice for others as long as they are the ones killing themselves.
But anyway, it has been said, nature does its job well, when humans can't sustain themselves anymore, they will die or stop growing.
If you are concerned about biodiversity, it's your human concern, not that of nature, nature is just a self regulated system, the fact that human expension is the cause of it just means we are more efficient (for now).
If you believe humanity is worth sustaining and would rather not having all of thus die suddenly from lack of resources there are solutions :
-encourage developing countries to reduce their natality and develop through the use of renewable energies unlike what countries that developed before did. Go work there on projects for that.
-chose what you eat and use in accordance to their impact, get your own energy from a solar pannel or whatever, if you can afford it.
Otherwise, I have to say, I very much agree with everything haphazard said.