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My reasoning as to why Mileena shouldn't be faulted for her Tarkatan nature and cannibalism:
It's fairly easy to understand that Tarkatans can only eat meat, and are therefore strictly carnivorous. Canonically, the Tarkatans rely on the "Flesh Trade" for food. In MK11 it's explicitly shown in both story more and interactions between Kitana and Baraka. Biologically their massive teeth and specialized jaws are well suited for a strictly meat diet.
Tarkatans are both nomadic and warmongering. They'll wage wars with other Tarkatan tribes and renew their resources in doing so. But more importantly, they renew their food supplies.
Regardless of morality, it stands to reason that due to her Tarkatan heritage, Mileena cannot eat regular food. Whether she can't digest it or can't handle the taste of regular food, that's up to the audience to decide. Personally, I doubt that Tarkatans, and by extension Mileena, can eat regular food.
While I can't defend her voracious and ruthless appetite, I can defend her need to be a cannibal. After all, it's what she needs to do to survive.