I Have a Confession - I Killed a PC

It happened on our last session. The party was facing a boss, a defiler who had just finished a ritual to transform him in some kind of demon draconish sorcerer, and they were winning by just a little (two of six were down and making death saves).

The boss was with just 30 hit points when he decided to make the run. He managed to escape through the door and run through a corridor leading further in the dungeon. When he ran out, the party didn't chase him, they choose to stay together and heal the dying and the poor child used in the ritual (they had to pass through a skill challenge to save the child's life). I should have said the majority of the party, the barbarian decided to run after him and end this once and for all.

The defiler seeing the barbarian chasing him, alone, turned back and fired his necrotic bolts at him. The barbarian dropped and the boss ran away. At that point the group was in the middle of the skill challenge to save the child's life, trying to remove all the necrotic and demonic energy around the kid. They did heard the cry of the barbarian when he was hit and fell, but they had to choose, they would either run to save their companion or the child. They trusted the barbarian would not fail 3 death saves too quick and would be able to save him after the kid, but they were unlucky.

The child was saved (although it cost the infection of a demonic force inside one of the characters), but the barbarian died, he failed 3 saves in a row, he was dead. I killed a character, and it wasn't that difficult as people say it is in 4th edition.

At that time I felt like I had won something, I was kinda in the villain mode, so I was excited he managed to escape and take someone out. But a few minutes later I was worried, I just killed one of my player's character. Is he upset? Will he be willing to make another one? Or will he be hating this game now?

Luckily for me he was planning to make another character anyway, so he was not that upset (although I  think he wasn't very happy). All this made me think about character deaths in my games, how they happen, if I kill too many of them, if I over-challenge the party and stuff.

First of all, I am not an enemy of my players. More than ever I am trying to make the best game I can for them. We decided what kind of campaign we wanted to play together, I made custom character sheets for them, I am making handouts, I am really trying to make them enjoy the game as much as I can. And as far as I can say, they are liking it.

On the other hand, I can't just give them everything without any challenge in the game. I want the adventures to be challenge and to test their resources. I think the adventure needs to have risk of death and failure, specially in important fights, such as boss fights. The characters should know they are facing very powerful creatures. They can win, but they can also lose the fight, and die.

I don't know if this is wrong, but I have a feeling that the final battle, the fight with the boss, has to be harsh. So if I don't see one or two PCs almost dying I am not satisfied. I don't actually want to kill them, but I want them to think I want to. They don't need to drop down, but if I don't see them with less than 10 hit points, crying for healing and help, I think the battle was not worth to be the final fight of the adventure.

Maybe this is wrong. Maybe if the players use very well thought strategy and good resource management they could breeze through a hard encounter. But would that feel right in the story? What would be dramatic about it?

I have to confess that I have a bad reputation as a DM. They think I am an "Evil DM", that I kill characters for fun. I believe that this is more of a joke than an serious reputation, but as far as I can remember, characters die on my games, but I think that's almost always their fault.

I usually say to myself that I don't kill PCs, they kill themselves with bad decisions, or without thinking of consequences. But is it really the truth, or am I fooling myself? Am I a PCs serial Killer?

Either way, my group seems to like my adventures. And that's enough for me. I have fun, they have fun.

And you? What do you think of all this? Should the heroes face death constantly at their battles? Should there always be a risk? Or should they be undefeatable? Able to face any challenge without fear and need of well thought tactics?