I will note that this is one of the fundamental failings of utilitarianism, the "mere addition" paradox. Basically, take a billion people who are miserable, and one million people who are very happy. If you "add up" the happiness of the billion people, they are "happier" on the whole than the million people; therefore, the billion are a better solution to use of natural resources.

The problem is that it always assumes some incorrect things:

1) It assumes all people are equal 2) It assumes that happiness is transitive 3) It assumes that you can actually quantify happiness in a meaningful way in this manner 4) It assumes the additive property for happiness - that you can add up some number of miserable people to get one happy person.

None of these assumptions are necessarily true.

Of course, all moral philosophies are going to fail at some level.

Note that, for instance, in this case there is an obvious difference: adding 50 years to one life is actually significantly better than extending 50 lives by 1 year each, as the investment to improve one person for 50 years is considerably less, and one person with 50 years can do considerably larger, longer, and grander projects.