The fairies of old weren't cute little bewinged pixies who fluttered happily around humans. Elves didn't make children toys or live deep in forests with no interaction with mortals. Often, they would interact with humans with no thought to the consequences of their actions, or they would be tricksters that deliberately delighted in the utter mess they made of mortal lives (such as the classic character Puck from A Midsummer Night's Dream). At worst, they're like serial killers with magic.