TL;DR OP doesn't consider the creation of new knowledge and thus predictions of what happens decades into the future will be misleading, or outright wrong. The Beginning of Infinity (2011) offers a deep and comprehensive argument as to why the 'end' OP predicts will never happen, or at least only under some circumstances, one of which is ironically what OP actually advises as a solution (reduce population, become sustainable). It also is an excellent theory of epistemology, and so much more.
I don't think we have a moral obligation to 'save' the third world, however I disagree with /u/TheMer0vingian's argument.
The news that earth's population has already exceeded its sustainable carrying capacity is nothing new.
You are correct. It is particularly not-new: this has been "true" for over 300 years... look to Malthus; his predictions on food-production-cliffs and the like have never come true. Nor the same predictions made about peak oil. Or, come to think of it, any of these sorts of predictions.
Predictions of this sort often rely on not solving problems, which, when one thinks about it, is an excellent way to prevent a society from continuing.
Global population continues to climb exponentially, accelerating the rate at which resources are depleted.
Again, happening for 300 years. Won't even get into subtleties about decelerating growth. If one wants to carry this line of reasoning one need to explain a lot about why everyone in the past was wrong. IMO this is the intelligentsia's "the end is nigh" argument, and just as wrong.
(from regions with the highest birth rates no less)
Also the highest disease rates, and child mortality rates, and whatevers. Our explanations for these rates concern the context of the people quite a lot, and so to disregard the change of context in the main argument is a little cheap IMO.
By intervening and taking in millions of destitute people we [...] are in fact causing the deaths of billions of future humans, and quite possibly the entire human species, by facilitating the continued unchecked population growth that continues to consume earth's natural resources at an unsustainable rate.
This doesn't follow. Moving lots of poor people to rich countries isn't going to magically keep people reproducing at the same rate. Other economic factors will begin to apply and things will reach equilibrium again.
We've always used natural resources at unsustainable rates. Just think about that for a moment. Hundreds of years of 'unsustainable' rates, yet, here we are.
It is no longer a question of if, but when, earth will run dry of resources. It's a statistical inevitability.
Completely disagree. Malthus made the same argument in the late 1700s. Statistical inevitability that never eventuated. The reason is that people kept solving the 'next' problem. There is a technicality under which OP is correct: the Earth is finite so realistically there is a point where we convert the entire mass of the Earth to energy but since this implies an advanced space-faring species I don't consider it inside the domain OP is talking about.
We are compassionate beings by nature, and it sounds callous to say, but logically if we truly seek to minimize the loss of life, is it not a better long term strategy to reduce the population of the earth ...
No, and I don't think minimising loss of life is a good way to think of this anyway*.
Let's think about maximising gain of life instead, and turning those future-people into people. To do that we should focus on solving problems, and increasing the population that can solve problems. This is (luckily?) the path we're on.
The argument over all is a bad one because it doesn't consider the creation of new knowledge (moreover it assumes no new knowledge is created) and you can basically use the argument at any time to justify whatever you want (eg Malthus / Peak Oil).
* If one's goal is to minimize loss of life the best plan is to just kill everyone today. That way only 7 billion odd people will ever need to die again. Even if one don't like this idea and want to go by 'minimize violent loss of life' one still has to consider that on an infinite time line there will be an infinite number of people that fall victim to this, certainly more than 7 billion if humans achieve their potential, and so one has the same argument.