Even if I sound like an armchair general with this...

Treating one's enemy with respect, as at least one's equal, is a necessary thing. If that is not done, the enemy may be underestimated, and that leaves one open for so many problems.

Probably worse, dehumanizing one's enemies leads to one's own dehumanization. In battle, moral high ground is no less important than the physical one.

Churchill once said, "When you have to kill a man it costs nothing to be polite".