We may not need to contrive some reason why saving lives will actually save us money, and therefore saving lives is good.
If you need an economic reason to save lives, you will have to do incredible gymnastics to justify medical treatment for old people, for instance.
So don't do the acrobatics. We can just say that medicine is good, actually.
Economics is devilishly difficult to really efficiently predict. More reliable lifespans and a larger elderly population can affect the total flow of money in ways nobody can properly imagine, positively or negatively.
From a younger perspective, the effect of eliminating cancers from the equation implies a lot. What is more expensive to the world, years of cancer treatments and palliative care to somebody in their 70s, or somebody living healthily through to 90 years old before dying from heart failure? What about the family cost of caring for a sick elderly relative?
Write longer posts in paragraph form that use positive language if you wish to successfully convey complex ideas.
Or don't and people will just think you're a shallow dick.