Furthermore, death comes at a huge cost of losing the accumulated knowledge of all those people.
Really, "cure aging" is the same as "cure cancer" or "cure diabetes". Disease prevention is just a shortsighted version of curing the problem of aging in general.
Prove it to be a net gain, when the negative side of the equation is the death of billions.
You can make anything look good by considering only the positives, or vice versa, but it's no way to make decisions.