I am a student of philosophy via cultural anthropology. This means that I study socio-cultural evidence from the past and from outside our civilization, as a way of understanding ourselves.
The first thing to be realized this way, is that as individuals of the human species we acquire a sense of personal identity by education in a particular society.
Two things to be noticed in what I just said.
First: the awareness of humanity, as a belonging that transcends the society in which we are born and raised.
Second: the fact that it is still in the education we receive in our society that we become aware of the larger humanity to which we belong.
How are we supposed to look at the humanity of those who do not belong to our particular society? This is the question that cultural anthropology raises.
There are two possible answers.
One, is that men are as such individuals of a species, identical as far as nature goes, but made different by culture.
Cultures, then, would be things on which the science of man, i.e. anthropology, cannot bring any judgment. Neither could do it the law, because it grants to everybody the right to his own opinions, and in this understanding cultures are nothing more than opinions.
The second answer, which I think the correct one, is that culture is nothing else than the knowledge proper of a society, with its way of accounting for what makes people belonging to it different and yet, we would say, sharing the same humanity.
In other words, the vocabulary of anthropology, with the distinction of "nature" and "culture", informs our way of thinking ourselves in relation to others: makes our culture.
If at this point you should have the impression that my talk becomes convoluted, like a snake biting its tail, you are right: it is the reflection to which I am forced if I take what other people think of themselves seriously.
If I make of their thinking a culture, meaning an opinion, then, either I push them outside of true mature humanity, or I have to recognize that also mine are just opinions. If I take it as knowledge, then I can engage with them in conversation, to see what might be true or false in it compared with what I know, and vice versa.
The question, for every society, is where the threshold of humanity lies: whether foreigners, living beyond our borders, or for that matter inside our borders, are susceptible of being equated with ourselves, and in what they might be so equated.
If we think, as in our particular society we do think, that they should be equated, we can't deny humanity to people of different culture, but precisely because of this we can judge and eventually refute their culture if it implies negation of a common humanity.
All that I said about culture, I could equally have said about religion.