> This sort of leaves out the reality that decomposing bodies are a critical part of the ecosystem
Buy fertilizer. Of all the possible attempts at arguments that could possibly be raised in support of letting people continue to die, the last one I'd expect is "those human lives are more valuable as rotting corpses to fertilize plants".
> If/when you have reasonable solutions for overpopulation, massive resource consumption by advanced societies, and pollution, then we can talk about longevity.
1) There are documented studies that people have less children and do so less quickly when they feel safer. And in any case, it's a very big universe and this is not a reason to let 150000 people die every day.
2) We can and have built more efficient ways to make use of resources, and we will continue to do so. Killing off humans is not a reasonable way to solve resource consumption problems. The primary problem of excessive resource consumption is that it threatens human lives, which makes it utterly self-defeating to argue that humans should die so we use less resources.
3) Pollution is a serious problem. We've only got the one planet (for now), and we need to take care of it and make sure it continues to support life and help life flourish. So by all means let's solve that problem. Fortunately, we've got billions of people, and we're capable of working on multiple massive problems at once. (You might also recognize that one of the biggest problems with pollution is people not acknowledging it as a problem; there's a parallel here.)
4) People will continue to talk about longevity, and more importantly actually work towards fixing the problem. Once people understand that we can actually do something about it, consciously choosing to not do something about it is a choice measured in lives lost, and inaction becomes far less excusable. Trying to stop other people from doing something about it is tantamount to murder, in much the same way as trying to stop a doctor from treating a patient.