I've noticed that all ideas I create usually have sadness attached to them, or violence. My stories are generally violent, containing lots of harm to characters (emotional/physical) and death as well. I like killing off characters, but I also really enjoy fleshing them out first, of course. I really appreciate a nice impactful loss. I like ending my stories in tragedy, so that may be the reason for all the negativity attached to them.
Alas, I really don't like killing off my characters (especially not my MCs). =\ I don't mind giving them superficial or even serious wounds, but I like building rapport and banter between my characters - it's so much fun - so killing them goes against that fun. Maybe I'm just too tender-hearted?

I also don't like ending my stories with tragedy. I'm all for the MC experiencing a good change-arc that changes them in some way, but I also think the MC should be rewarded with a happy ending. (I love a happy ending).

Having said that, I've had one or two novels where one or two of the MCs friends dies (it's usually the Big Lummox With The Heart Of Gold(TM)), which gives my MC extra motivation to fight harder against the Jerk-Ass Antagonist. =P If that sounds familiar, it should; it happens a lot in movies, because it usually works. (But I invest a lot of thought in creating that Big Lummox, so it's obviously sad when he dies). =\