Thanks for your comment. I think you may slightly misunderstood what I was trying to convey, or I may have not been fully clear. I said that it may not be advisable to expose younger learners to the cross-cultural learning material that is often prepared from the perspective of a "hostile critic" because their minds may not be mature enough to fully understand the reasons for such a criticism. And they may simply end up with more prejudices and biases toward another culture, or their own.
And as for the other point, I don't think cross-cultural learning has to be introduced only as a separate subject (though in higher levels of education, such a subject may be there for those interested to pursue such a study at deeper level). In middle school, high school and even undergraduate education, a meaningful crosscultural study can be made a part of every subject stream, including sciences. It is a matter of creative presentation of the study material, for the most part.