In this episode (https://www.samharris.org/podcasts/making-sense-episodes/abusing-dolores) Sam Harris argues (as he has many times before) to Paul Bloom that moral blame is irrational in that it is impossible to blame someone once the truth of determinism is understood and hence it is understood that they couldn't have done otherwise.

Can this argument be correct if we're interpreting blame to be an emotion?

Though we have some control over our emotions in the long term we really don't choose them in the short term and generally speaking even when we do choose them that choice is not typically done within a hyper-rational framework although perhaps in principle it could be. To the extent that emoting in a particular way is viewed as an agential behavior it should be possible to at least intentionally calibrate our emotional responses in a rational way.

However I don't think that Sam is arguing that the practice of blame in general is going to have greater costs than benefits. His argument hinges on the premise that moral blame is predicated on the idea that the transgressor possesses libertarian agency (not sure if this is a term but I mean the type of agency which an agent which had libertarian free will would have). Therefore he is saying moral blame is irrational in the sense that it is a consequence of an irrational belief (the belief in libertarian free will). This strikes me as very odd that something which human beings seem to do innately could be predicated on something which in his view (and mine as well) is not even a coherent concept. When I think about blame from a first person firsthand perspective it also doesn't seem to be predicated on libertarian agency.

I suppose it's possible that all he really means is that if one really understood and accepted that a particular transgressor couldn't have done otherwise in the most general sense then it would simply be impossible to blame them. If we view this as a phenomenological claim then it seems at least plausible to me except that I think perhaps there are two types of moral blame which can be differentiated by their function. The function of the first type is to facilitate some sort of behavior modification algorithm in order to correct the behavior of the blamed. The function of the second type is to simply identify the transgressor as an enemy of the social group to facilitate the removal of the transgressor. The second type of blame seems possible even without any conception of agency at all. In fact it is possible (although generally considered wrong in our society) to blame someone specifically because of their immutable characteristics.