In America, we don't eat cats or snails or brains but a lot of food choices are just cultural.  So it may be with afterbirth.

Placentophagia may offer benefits to human mothers and perhaps to non-mothers and even males, according to a new study in Ecology of Food and Nutrition. Hey, they have devoted a whole issue to Placentophagia so it must be important.  

Placenta ingestion, and amniotic fluid also, by non-human mammalian mothers provide significant benefits, they say; like mother-infant interaction and boosting the effects of pregnancy-mediated analgesia in the delivering mother. Mostly, they say it potentiates opioid circuits in the maternal brain that facilitate the onset of caretaking behavior, and suppresses postpartum pseudopregnancy, thereby increasing the possibilities for fertilization.

In other words, the real benefits are not anything that can be measured, just surveyed by psychologists who want to find a benefit. 

So maternal hostility is physical and placenta may help?  Well, maybe, but that is the problem. They don't claim it does, they claim it might, and someone should study that empirically.  

Afterbirth: Study asks if we could derive benefits from ingesting placenta Science Codex