If I may, I will give you the words of
Dr Shehzad Saleem, an Islamic Scholar with the Al-Mawrid Foundation.
Question:
I would be grateful if you could enlighten us on the subject of cannibalism and Islam.
Answer:
Islam has not made a comprehensive list of edibles which are prohibited to consume simply because human nature (if not perverted) instinctively knows what to eat and what not to eat. The innate guidance Islam provides human beings in this regard is enough to show them the way. As per this inborn instinctive guidance eating human flesh is something which is a detestable and abhorrent practice.
According then to Dr Saleem, Humans have an inborn instinctive natural abhorrence to eating Human Flesh. We simply innately know it is wrong......well, that would surely apply to all Human Beings, not only Muslims, I mean a Muslim is not another species after all.
So your justification applies to everyone, regardless of whether they are religious.