The argument fails anyway because science has arguably saved more people than it has killed.
What does this mean, exactly? Who has been killed "by science"? In the entire history of the world, all murder victims were killed by people, regardless of what technology they used. Accidental deaths are much like deaths from natural causes; people die. It's a part of the universe. Some people just meet their end sooner than others. Someone could be healthy until they are a hundred and thirty, while someone else can die of disease after three months.
But even if it were not, if we were to say.. know that some breakthrough capable of saving infinite amounts of life has and is being actively withheld from us as a direct consequence of science's being - well even then it wouldn't matter. Science has still saved more lives than no science has. The withheld breakthrough is irrelevant because without science there would be no breakthrough to withhold. Ie it's a non factor for both the options.
And are you trying to say that "saving infinite amounts of life" - that is, immortality, for the entire world - would be a
positive effect of science? Overcrowding is one of the world's biggest issues. If nobody ever died, we would either have to start killing people just to make room or all of humanity would be absolutely miserable. Neither of those sound like good outcomes.
Do we really value human life so much that we're measuring the morality of science based on how many people we can keep from dying? A number which is, at this very moment, zero, and to increase it beyond zero would be to spark the end of civilization. People living healthy lives is good, yes. But they need to live, be happy for x amount of time, and then
die, to make room for new people. And no, maintaining an immortal population while the birth rate decreases to nothing isn't the solution either. I don't think I need to explain why.
Perhaps in the distant future, when extrasolar colonization is feasible (
if it ever becomes feasible), the prevention of death may be a less impractical concern. But until then, as a species, we need to accept mortality. Death isn't
bad. It is something that happens. It's a natural part of existence. To fear the unknown to that great a degree is a problem.
Also: Who wants to live forever?