I don't particularly subscribe to romantic notions of causes worth dying for, but you can still die for a cause if aging isn't a thing. I daresay cannon fodder will exist, in some form... and it will be romanticised in the same way.
Causes worth dedicating life to... that tends to be more useful than dying for causes. In that frame, you have more to give if you have more life.
For what it’s worth, I used to find the arguments that we should put the brightest minds on space exploration over eliminating suffering as concrete, but nowadays.. can’t say they those arguments seem as watertight.. saying that as someone whose hands have touched some of these projects. Curious if others feel the same way or have points to make in the opposite direction
We're better off approaching them either more broadly or more narrowly. IE, we can dedicate resources to tighter goals, like reducing childhood mortality... a horrendous thing that most people suffered for most of humanity. We really made a lot of progress on this.
Alternatively, we can think of it more broadly... advancing as a species, culture and society. In that sense, space travel is a good idea.
Tackling the elimination of suffering head on is likely to resolve to "be a politician/priest/lawyer" or somesuch.
In any case, I think the mistake is thinking of everything as competitive, at a broad level. Rather, people tend to see ambitious, "humanities' first" goals as competitive with "eliminating suffering" or other broad goals. It's rare to hear people think that sports or cinema are competitive with the elimination of suffering.
That sounds a lot like propaganda line from a book of previous victors who got to write the history.
While I think you are not completely off - there were just undertakings that needed sacrifice of human lives - this line of thinking seems to be stained forever through constant cynical abuse by the powers that be and powers that aspire to be.
Now we scroll through feeds and pat ourselves on the back for increasing the average lifespan. No one asks whether these long lives are even worth living.
No one asks why progress for the sake of progress is inherently good.