At the risk of repeating myself: imagine a world where everyone was ageless by default, and they started to experience issues like inequality or overpopulation. What would that world's top scientists come up with? Would it be "kill everyone above a certain age"? I doubt it, because that would be very silly, and anyone seriously suggesting it in that world would be considered obviously insane. There are a lot of better options that don't require mass early death; these problems aren't inevitable.
>there's always the heat death of the universe. There's no escape from reality closing, you'd probably have a difficult time sustaining biological life-forms long before the universe is dark and cold. I doubt it would be pleasant.
This has always struck me as a very, very odd argument. Assuming protons decay, we're talking ~10^37 years until physics starts getting in the way. That's 10^27 times longer than the age of the universe. An entity observing those timescales would have time to see entire solar systems grow, mature, and die a billion billion times over, without exhausting even a billionth of that duration. Sure, such an entity would run out of stars to observe, and biology would get tricky, but computation wouldn't cease, and fundamentally that's all that's needed for a rich existence. It's an eternity nested in an eternity nested in an eternity. And if protons don't decay...
It's not infinite, but as a human, the distinction is completely irrelevant. Whatever a human would become on those timescales can decide what it wants to do later- for now, I'd just like more than a measly 100 years. It's not like we're wishing on a monkey paw.