Arthur Quiller-Couch was the one who initially advised writers to "Murder your darlings" in a 1914 lecture at Cambridge. He didn't mean characters. He was talking about extraneous ornamental writing that, while you're so very proud of it, does nothing but bog down the narrative. It has since been extrapolated to encompass the killing off of developed characters, and no one has run more amok with the idea than George R. R. Martin. There are better, less cheap ways of pulling the rug out from under the reader/viewer because you will inevitably numb your audience out, leaving you nowhere to go. I'm saddened to see Star Trek following the crowd this way.