One can never know what they are capable of until the situation presents itself. Sacrifice is a strong word that is tossed about carelessly these days. Taking something from someone else to benefit yourself is not a sacrifice.
Read the story of Richard Parker and Tom Dudley. Is what Dudley did defensible? What would you have done?
Dudley told the others that it was better that one of them die so that the others survive and that they should draw lots.
If Dudley thought it to be a good idea that one should die in order to save the others, should he not be willing to accept the fate of being that one? Did he choose Parker to be the one because he was in poor health or because he was too weak to fight off an attack? If he had waited until the man died before consuming his flesh, I would find it easier to defend his actions. That he decided the blood and meat would be more palatable if it were fresh, shows less desperation then the men reported. There is no justification in taking something from some else to benefit yourself. Perhaps Dudley should have considered chewing on this own limbs first.