To me fear of death is a sign of not really having been born yet. If you can't make 50 years worthwhile, you can't make 50000 years worthwhile, and if you can't cope with being limited to 80 years or so, you will not be able to cope with the heat death of the universe. It also stands to reason that if you feel it's impossible to give up 100 years of grown personality and memories, it will be even harder and more painful to give up orders of magnitude more of that. It seems like power in that those who want it the most deserve it the least because they are the worst at using it.
On a very basic level, if I feel myself to be entitled to live forever, then I couldn't rightfully deny that to anyone else. So at some point this would mean less new births. If it didn't, it would mean an even more crass explosion of the human footprint, an even more extreme choking out of other lifeforms -- and it could very well mean both. But that would suck, since being healthy and alive isn't just great because I can see 5000 million particles rendered in 3 lines of CSS, or watch the clouds go by, it's also because of the flora and fauna, and because of other people. Beings that surprise me, that come into the world and "become". Knowing there will be future question marks born is something way more sublime for me than "attack ships on fire" or having this one video that got 7234 million views.
Life isn't just me, it's also a river in which I am a drop. If I want to not be a drop, so I can keep seeing the river, well... if everybody does that, there is no more river, and if I want to reserve immortality for just myself, I am an asshole. I don't mean to brag, but I figured that out as a kid, and no immortality advocate I read or heard or saw so far managed to put a meaningful dent in it.
Yes, I am for medicine, I think it's great when people can live longer and stay healthy longer (even though we then ignore their wisdom when it's inconvenient, e.g. [0]), but no, I cannot draw you an exact line, except that I know "immortality" as extreme and as espoused by technophiles or emperors or preachers does not interest me, at all. If anything I'm curious about the biographies of the people looking for it; they point at some clouds that may or may not have a moon behind it, but I can't help but look from the finger to their arm to their shoulders to their head. I feel that's where the majority if not all of the action is.
Last, but not least: even if you managed to completely overcome all aging and disease, assuming no asteroids and other surprises: the only way to ensure you will live "forever" is to severely restrict the agency of anyone else but you. Other humans acting would be a potential threat, in infinite time it would become an infinite threat, while at the same time you have an infinite lifetime to lose. Nothing might be too crazy and machavellian, and like junkies people might just keep going down the spiral long after they lost all joy in it.
[0] https://news.ycombinator.com/item?id=17721280 <-- 99 years...