Indeed, martyrdom is not the same as sacrifice, given that the first mainly involves the free will of the sacrificed one. Nonetheless, the argument of the OP is that human sacrifice is faded to disappear because it isn't rational.
Martyrdom isn't either. It also involves the destruction of the capacity of a body. Indisputably, both situations had very different social costs and effects, but they are submitted to the same utility cost regarding a given society. That is to say, it doesn't matter if the man was a martyr or sacrificed by his kind, he is not useful as workforce. So, the "rational" argument doesn't convince me.
Martyrdom may not be rational, but it's irrational in a very different way than human sacrifice. That is to say, in human sacrifice, the person carrying out the sacrifice both makes the decision to sacrifice and pays the cost of losing whatever value the sacrifices could provide to him or her, while in martyrdom the martyr makes the decision to martyr themselves (that is, not to take action that could prevent them from being killed) but does
not pay the societal cost. Hence, there's a direct incentive for the sacrificer to reduce the amount of sacrifice, whereas there's no direct reason for the martyr to avoid martyrdom.
Furthermore, there is a rational reason for
other people to promote the ideal of martyrdom, which is that it serves as a very powerful demonstration of the attractiveness of a faith; if it is so compelling that people are willing to
die for it, after all, it must be a pretty great thing, right? Certainly enough to spend a bit of your own time on. Internally, it's great for creating an "us-versus-them" narrative and bringing members of a faith community together against outsiders. Hence, it's entirely rational for the church to glorify martyrdom and convince people that it's a good thing, whereas with human sacrifice there's much less incentive to keep large amounts of it going (small amounts may have similar benefits as martyrdom, but large amounts are economically damaging and may have other negative effects). In fact, to support this hypothesis, it's worth pointing out that most churches discourage
deliberately seeking martyrdom; being a martyr is good, but sacrificing yourself is not. Hence they can get the benefits of martyrs without paying the costs of having too many martyrs (i.e., the church literally dying, losing supporters, and so on).
It's also worth pointing out that societies where there were many martyrs tended to change in ways that reduced the number of martyrs eventually, though admittedly often not by choice.
