Two sides of the same coin generally means complementary items that may seem unrelated, not opposites. An English teacher I had banged on about theme and style

Two sides of the same coin generally means complementary items that may seem unrelated, not opposites. An English teacher I had banged on about theme and style being two sides of the same coin when writing. The example here would be that mass murder is not really as effective without technology, whereas technology enables us to flip to mass murder quickly even if we previously didn't consider it. They are complements.