....because it will get too dark too fast.

You don't want it to feel cheap. Character deaths happen, because real life deaths happen, and if you want your story to feel real, it can't be 100% kittens and sunshine. But to just randomly kill off characters (unless it's in a heavy war situation or something) is a cheap ploy, IMO.

I don't kill off characters unless it moves the story along, and don't kill every sympathetic character. We need that, like in life, but in life, good people also die, so they can, but please, killing everyone for no reason is pointless and will leave readers asking "why?"

Sometimes, it may be required for your plot, but I generally avoid doing it and I'd also advise others against it.

I think that there needs to be a good reason for it. It loses impact if it's done purely for shock value.

Not if it's out of the blue. Like bam you're dead or my god, they killed Kenny!

Never is. I'm sick to death of shock value deaths.