How can hatred not cease by hatred? It sounds incoherent

> “Hatred does not cease by hatred, but only by love; this is the eternal rule.” This quote by the Buddha makes no sense to me. Firstly and perhaps tangentially, it speaks of an "eternal" rule, but anything related to humans and other living beings including transcendent (who are the only entities that can experience hatred - inanimate rocks can't) are not permanent according to the Buddha. But okay, leaving that aside, two questions arise: 1. Why is hatred something that one should strive to cease? Clearly it involves important psychological functions, and had an evolutionary benefit. 2. How can hatred cease by love? If I love someone from another group, and that group hates me and wants me dead including any particular person from what group, they will be stronger and more motivated to destroy me, and so there will actually be less love. Moreover, there are many cases in history where two tribes hated each other, and one exterminated the other one, and the result was no more hatred. So hatred ended up ceasing through hatred. If someone could help me on these two points, I'd appreciate it.