I can think of a couple of differences:

The poor people during a famine at least have a fighting chance, if slim. Somehow, by hook or by crook, attain money or food, or leave for a region where there is no famine.

Also, a famine is a matter of public knowledge, which allows the possibility for a society to collectively (or fragmentedly) come up with a solution. In the torchwood scenario, [small spoiler warning] the true nature of the threat and the solution devised by the executive branch were being kept a secret. In fact, they were actively suppressing groups who were moving for alternative stances towards the alien threat. If it were public knowledge, the to-be-sacrificed class would at least have the option of revolting against the powers/system/'algorithm' which was mandating their extermination.