Is there some kind of rule here that Anthropology professors have to say that sexualization of the human breast is purely due to socialization in a way that makes me feel bad for jacking off to titties?

Both my Bio and Cultural Anth professors have done this, like WTF man. I also want to say, for the record, that whether or not that is the case, there is nothing inherently wrong with or weird about doing so, because fetishization does not have to lead to objectification. Also, I think it is possible to sexualize the breast in certain contexts while still not stigmatizing public breastfeeding. We don't have to be puritans.