The premise that human lives can be treated in straightforward arithmetical terms (e.g., that two lives are twice as valuable as one, and twelve are three times as valuable as four, and so on) seems to me to lead to some disquieting places.
Specifically, it seems that any time we can definitely save two lives by killing one person, we ought to do so without hesitation, or at least seriously consider it. Yes, there is damage done by the killing—grieving loved ones, the loss of a good chef—but if the value of a human life is as high as we tend to think it is, it probably outweighs that damage. If six people will almost certainly survive with organ transplants, and will almost certainly die without, and the only match is the taxi driver outside, then get her on the operating table ASAP. If any of the sick people are paramedics, or if the taxi driver tends not to pay her credit card bills, then let us move all the quicker.
The only barrier to such behavior would be a demand for greater and methodical inquiry into the precise value of a human life, the bearing of personal factors on that value (age, health, quality of life), and the overall effect of whether particular people live or die (a person might be more worth saving if they are working on a cure to a deadly disease—but also if they are a pillar of the community, and whose death would tend to cause depression in those around them). And if this barrier is the only thing standing in our way, it would seem that we ought to be doing everything we can to overcome it, so that we can get started on the proactive business.
I have a related question, as one still new to lesswrong: are there existing sequences on the philosophy behind/connected to utilitarianism, by which I mean, the notion that human lives, or life in general, has value? I assume there is either a sequence regarding this, or else a consensus which is generally accepted by the readers of this site (a consensus which, I hope, is nevertheless written out somewhere).