Let's keep this fairly short, as an excess of words will not make the points more compelling. There is a simple series of logical steps pursued below. Also, please note that I bring religion into the discussion because I have seen innumerable online dialogues where some participants claim that God wants humans to continue to create more and more people on the planet "for the greater happiness of all humanity". This idea, which I consider to be sadly deluded, is discussed somewhat below.
1) If the population keeps growing and resource use per person keeps growing, will we ever hit a limit on the planet's ability to supply everyone? And even if we limit average resource use per person, if population keeps growing will we hit a global limit at some point?
2) There is clearly a limit - if the entire surface of the earth were covered with people on every square foot, it would be impossible to feed everyone. So there is a limit, but there is some disagreement about where the limit lies. Therefore the answer is "yes" to #1. What do we do about that?
a) wait for the crisis to hit and then deal with it in the midst of war, hunger, and disease, or
b) plan ahead
3) For #2, a) might be OK if a God will take care of everything, but that is not good enough if you happen to believe that God helps those who help themselves - i.e. no one has asked you to turn yourself into a fool. So, unless one falls into the a) group, we are left with group b) i.e. plan ahead
4) Planning ahead: Is there a clear sign of when we will have these resource problems? Those signs might be shortages of fresh water, shortages of food, and wars over fertile territory water, oil, and other resources. Hmm, that sounds familiar. With all animals (and people are animals, at least in the sense that we need food and water, and shelter), overpopulation leads to disease, hunger, and/or fighting, and eventually shrinkage of population. How far away is this collapse, then, a) less than 100 years, or b) 100 years or more?
5) We don't know the answer to #4 for certain. In that case, let's use the probabilities to help our evaluation. If there is a 20% chance of terrible catastrophe in less than 100 years, or even a 10% chance, or a 5% chance, should we plan for that catastrophe now as a a form of insurance, or ignore that situation?
Do you, the reader, have health insurance and/or life insurance? Theft insurance? Why should we not try to provide some insurance so that we and the descendents of today's living people also have a livable planet. Is that longer-term goal as important as our having personal health insurance or life insurance right now? If not, why are we bothering to insure anything? Whom is benefited by life insurance or inheritance? If we give our families or our causes money as an inheritance gift, but there is nowhere to live a good life, what good is that money? So the question is, should we gamble: a) yes, or b) no
6) If you answer a), if you feel we can gamble with the future of the planet, and that the children of today and tomorrow do not matter, whether they are yours or not, then we need to do nothing else, and go on living what to me seems an empty life with no future. If you are young enough, say under 50, you will likely also be subject to severe changes yourself. Those changes are already starting in severe form in some parts of the world with food shortages, and in all parts of the world with the price of oil and gasoline.
If like most people you answer b), if you feel we should not gamble with the future of humanity, then we need to act, to control population as well as to quickly start using existing resources much more wisely, and to cut use of resources where we can. This should be a priority; it increases the chance of humanity surviving through the next few hundred years in a recognizable form of society, while requiring only superficial changes of people today - drive less, turn off the lights when leaving a room, use floursescent or LED lights, turn down the thermostat (if you get heat), insulate, share and reuse all kinds of items... you have seen the lists. Eventually we will run out of fossil fuels, but we can transition to a new way of life, if we gives ourselves enough advance notice of the problems coming.
7) What about population? Even the Bible says people need to take care of the creation that is around us. And if one does nottake a religious view, we stillneed to take care of the very environment that keeps us alive
For those reasons, this ultimate mandate of caring for the planet would demand birth control, sexual, relationship, and environmental education, and other measures to prevent unchecked population growth, and to allow gradual reduction or perhaps redistribution of today's population. Many believe that when fossil fuels runs out we can not keep alive even the level of population currently on the planet.
Some might believe that it is best to see starvation, disease, and war, rather than use birth control. I believe that is a cruel delusion. Somehow that stance is believed to be embedded in holy books; but "be fruitful and multiply" could be a conditional statement, conditioned on there being a benefit to increasing population at the time those words were uttered. But one is not "fruitful" if people are being born into some degree of hapiness so that others can die or live in suffering. Most people would vote for trying to protect as many living people as possible rather than create further misery.
Conclusion:
8) For most of us, the inevitable conclusion is, or should be, to promote birth control and promote the principles of conservation and reuse of resources, to benefit the whole planet.
My lifelong pursuit, since age 18, has been to live more fully and find wisdom. This has involved studies with Zen masters, Tai Chi masters, and great psychotherapists while achieving my license as a gestalt therapist and psychoanalyst.
Along the way, I became aware of how the planet is under great stress due to the driven nature of human activity on this planet.
I believe that the advancement of human well-being will reduce societies addictive behaviors, and will thus also help preserve the environment and perhaps slow down the effects of global warming and other major threats to the health of human societies.