It's a natural ego driven thing to want to survive, but it is still driven by ego.
We've been seeking to and succeeding at extending our natural lifespans since forever. The only sensible argument against it is that the planet would eventually be overcrowded, assuming we don't become interplanetary any time soon.
What I'm trying to say is that all progress has occurred within our now millenia old system of relatively short lifespans. It means that within 150 years, societies can completely change because new individuals and experiences have to take over. Even the ancients saw death as a kind of leveler. We all die, even the mighty don't get to take anything with them.
Does that happen if we change that equation? Maybe it doesn't matter because people are good at adapting, but there's still a possibility it isn't all sunshine.
Or to put it in plain words and as I can't find a way to make it less confusing: why isn't your position equivalent to advocating for everyone to kill themselves (or at the least, not caring at all whether they live or die)