Killing off characters is a balancing act

Something that came up in my writer's group once  was the question all fiction writers face: when and if should you kill off a character.  Death is a part of life.  And really, if there is no risk in a situation, there is not much tension either.  Unless you're writing a romance where the two (or more than two, in some subgenres) main characters need a happy-ever-after (or at least a happy for now) ending, any character should be fair game to get killed off, right?

Maybe not.  When you write a story, you're asking the reader to invest their time and a certain level of emotional involvement in that story, and that means making them care what happens to the characters.  Killing a character for a good reason is one thing, but killing them off just to show that you're willing to do it can leave your reader feeling betrayed, almost like they've invested time in a relationship and then found out it could never have worked out. I had a friend who is also a fan tell me that when she came to the part of THE SIXTH DISCIPLINE where a major character dies, she closed her Kindle and put it down like it was on fire.

So what constitutes a good reason to axe a character?  I heard a writer at the Pikes Peak Writer's Conference (and I wish I could remember her name!) articulate the best rule I have ever heard:  you kill off a character to change the motivation of another character.  That works for me.  But I would also say that, if possible, it should not be as simple as their death making the protagonist mad for revenge or anything like that.  Certainly you don't want a female character to get horribly slaughtered just to motivate the male hero to a blood rage (a.k.a., "Women in refrigerators syndrome"). I always thought killing off the First Lady in the movie Independence Day was really just a milder variant of shoving her body into a refrigerator. She wasn't seen as necessary to the story (she didn't fly a jet or otherwise act heroically) and her death, conveniently staged in her husband's presence, motivated him even further to kill those nasty aliens. When I killed off the character that my friend complained about, I answered that he or she was in the way of the plot.

The revenge angle is not totally bad, but I think it works better when one character's sudden, abrupt absence actually changes the other character's circumstances.  Maybe now they have to support themselves, or rule their country, or face their fears, or go on a quest, or even just finally grow up.

Of course, in spec fic, an added complication is that magic/advanced technology may make it possible to bring the dead back to life, and I don't mean as zombies or anything like that.  I mean that spec fic writers have to be careful they don't make death meaningless.  That happened on STAR TREK TOS a little bit and TNG even more so.  The damn transporter got too powerful!  If a machine can basically copy a person's molecules and later spew out a copy on demand, no character ever needed to stay dead. 

So, have you ever read a book and gotten really angry at the author for killing a character?  Or have you seen an instances of too-powerful-transporter syndrome?  Alternatively, have you ever ready a story and thought (as was said at my writer's group once), "Really, the author should have just killed off x?"