Humans are really pros at sugarcoating. If you say old people should step down for the sake of new generations, it sounds so noble and rightful, doesn’t it? What it actually means, though, is ‘We value old people less than new ones,’ and this doesn’t sound very noble or rightful. This is plain and brutal survival of the species.
Kids are (generally) cute and helpless. This is what triggers our instinct to protect them, even thought it is not the reason we do it. A species relying on reproduction to ensure its existence wouldn’t last long if it didn’t care for its children. Even if we had already developed comprehensive rejuvenation therapies, we would still be mortals; if we stopped reproducing altogether and forever, we would still risk extinction, although on a very long timescale. (In other words, we could still die one by one of other causes than ageing.) It’s the reason children are important (to us and other species): They’re potential means of reproduction. Additionally, they need special attention, because they’re not able to take care of themselves and are thus more at risk of dying before they can reproduce. That’s why most species on the planet make such a big deal out of protecting their offspring—species that don’t are less likely to stick around long enough to tell the tale.
Individuals who are no longer kids but still are fertile are still important for reproduction purposes, but require less attention from others and from society, because they can look after themselves. Individuals who can no longer reproduce, or who wouldn’t be able to take care of their offspring even if they could have any (mainly elderly adults), have zero importance in this sense, because they use up resources of society without contributing to the survival of society itself. They’ve (assumably) already contributed to the perpetuation of the species, and now that they no longer can, they’re just a burden. Thus, from the cynical point of view of the survival of the species, it makes zero sense to dedicate any resources to the care of the elderly. As a matter of fact, besides humans, there aren’t many examples of species whose younger members look after the elderly of the family.
The lack of importance of the elderly as a means of reproduction is hard-coded in our evolution, just like the extreme importance of children for the same purpose. That’s why some think old people should just step down and make room for the young, but we certainly can’t call ourselves a civilised society if we listen to the brainless voice of a biological instinct as old as the world without thinking about its implications first. We don’t care for the elderly because of what they can or cannot contribute in terms of reproduction of the species; we care for them because they’re our people, and they don’t have to ‘step down’ for anyone.
Hang on, though. Let’s try and make a thought experiment. Assume the elderly did have to step down in favour of newer people. Just what people are we talking about, exactly? Certainly people who aren’t here yet, because people who already are here have already got room for themselves. We’re definitely not anywhere near the point when we’d need to kill off someone right after a new human is born because of lack of space, so the elderly don’t really need to step down for the sake of people who are in the making, either. It seems we’re left only with people who aren’t even in the making yet. Is it for them that the elderly should step down? That would mean the right to life of people who are already alive is less important than that of people who don’t exist yet. This kind of reasoning is the same as that of pro-lifers, who think that the right of choice of women is less important than the right to life of a non-sentient, brainless ball of cells—or even worse, some imaginary baby who could be awesome, beautiful, and what-you-have if you just gave up on wearing a condom and a bunch of other favourable conditions were met.
The truth is, there are no people to make room for. Existence is not like a ride in an amusement park, where people are waiting in line and it just would be so nice of you to let others get on once you’re done with it. In the case of existence, there are no people in line waiting for their turn, but just a bunch of chemicals scattered around that could eventually end up contributing to creating a person for a certain amount of time. (Most of your tissues don’t stay the same forever, and will replace themselves at a certain pace, varying from days to years.)
While I’m sure that one’s death would change things around enough to make a difference as to whether person A or B or none at all is eventually born, so does having sex with your partner tomorrow morning rather than tonight or eating certain things rather than others. Since such insignificant things can and do have an impact on who is born or not, it’s clear that worrying about people who aren’t even in the making yet is a waste of time, and certainly it isn’t sensible to prioritise the non-existent right to life of imaginary people over that of very much real and alive, breathing people.
Objections to rejuvenation
Objections to living ‘forever’
All answers in short