I think this is more a hypothetical, ethical talking point, rather than really considering letting people die. I sure as heck wouldn’t want to the person that actually made the decision to let all those people die, no matter what might be thought hypothetically.
Overpopulation, starvation and poverty are huge problems in the world today, and the advances in medicine and increased life-spans of people in the West does strike a rather tricky ethical question. Is it really right for richer people in the West to be doing everything they can to extend their life-spans while the rest of the world is dying because too many people are trying to live on too little food? Why should we consider us in the West to be so much more worthy of a longer life than the rest of the world?
In a purely ethical sense, I think it would be fairer if those of us in the West were to accept the fact that we have to die in order to make room for others and stop being so selfish.
One of the arguments for the control of overpopulation is the increase in contraception, but in much of the world having a large family is the only way to protect yourself from starvation, they need to have as many children as possible in order for them to help them on the land and feed the rest of the people.
In a hypothetical sense, I think it is much fairer for people that have had their lives artificially extended or are being kept alive just by medical expertise to lose their lives rather than young, healthy people (if one had to make the choice between them).