I’ve been watching Torchwood for the first time, and most likely the last. It has various problems: I find none of the characters except Jack engaging, there is little or no display of the kind of the competence that makes us love teams (Leverage!), and I keep getting the impression that Torchwood made things worse more often than better. However, it was early in the 2nd season (Episode 3) that I was able to isolate the biggest reason it kept irritating me.
Look at it this way: It is perfectly all right, sometimes, to have the audience emotionally engage with a character , then kill off that character. It can be cathartic, and it can also raise the stakes—it lets the audience know you’re serious, that no one is safe, that the danger is real, and so on.
If the only time there is emotional engagement you know that it will turn out bad, that there’s no chance of it working out, then all of a sudden you’ve lowered the stakes, usually to zero; I find myself saying, “Oh, look. It’s a sweet romance; I guess that he’s going to leave so I can feel all sad for her. Whatever.” Or, “Hey, an extremely likable character. He’s going to die. Yawn.”
Just as the possibility of sorrow increases the tension and makes us engage, if there is no possibility of happiness, we just stop caring.