There are weak, as in the elderly who have survived and children who have not been given the chance, or people who might have just had a bout of very bad luck, and the weak who are unfit to survive by virtue of their inability to become useful, productive members of society.
Techniques developed to save the former also save the latter, and vice versa. As a species, we would probably be better off with fewer of the latter. But who might be able to judge to whom treatment is given, and to whom it is denied? I don't think any human is qualified. A diety? None such exist, and if one does, it is certainly deferring its judgment until later. Our only choice is to help as many as we can, and hope the person we are helping belongs to the former, and not the latter.
Also, it's important to remember that while some deaths might be good for the whole, each death is also an individual tragedy for those close to that person. I only wish I could remember who said this.