But there is literally no physical law stopping us from letting every human on Earth now live until the sun dies, if we had the right tools.
Yeah, there are. The very limitations you say "the right tools would fix" are the very limitations of reality itself. We could make rocks exist forever if we coated them in some magical substance that prevented wind erosion, abrading, and all the hundreds of other micro processes that contribute to decay. I know, maybe if we made a field that just stopped proton and radiological decay altogether.
And humans could exist forever if hooked up to perpetual motion machines and were pumped full of intelligent nanobots that massage our neurons, build up the myelin sheaths around them to improve memory and thought function, and snap and reorder neuron pathways according to some master plan for peak human performance.
Just like I could be magically happy if I built a machine that makes everything I wanted true.
And then we remember what reality is, from the basis of scarcity, to competition, to logistics, to those pesky fundamentals some treat as minor obstacles....and we're back to where we are. A forum discussion about things no one is qualified to achieve. What if the nature of reality is that life, as we understand it, has to decay to function at all? That without decay, there is no motion, and therefore there is no life?
The assumption on the part of humanity is that our potential is limitless, that we can do anything if we have enough time. We know not our true limits because we haven't searched for them yet, and take that to mean there are no limits until we find them. The absence of evidence is not the evidence of absence, blah blah blah.
I'm not interested in what's not even theoretically possible yet. For all the talk about how lives are wasted in pursuits of this or that, intellectual masturbation about things that aren't even within the scope of our possibilities now is just as much of a crime against humanity as play Pong until you keel over in your chair. You could even argue the brain activity you get from thinking about the topic is a sort of 'monkey pressing the button' as we pride ourselves on how
deep we can think about reality.
Or simply put, life is one form of masturbation or another.