I really don't like killing players, and when I am a player, I really don't like having my pc killed. That being said, I like the idea of player killing, because then it ups the stakes (theoretically. I've never played in a permadeath campaign). Parties would have to think twice about taking on a more powerful foe, or consider running away as a very real option to avoid death, or reconsider doing absolutely stupid shit that will get them arrested and executed. It (again, theoretically) makes the game more realistic in a sense?
But then you're playing it, and your character you wrote a 3 page backstory for dies because of bad rolls or shitty combat balancing, and now you're pissed because you really liked playing that character, but the dm isn't going to rewind time and the party has no way to resurrect the character or at least preserve the body until they do have the means. Or you're on the other side of this as a DM, and watching a good player get pissed off and quit the table because of it.
In my campaign, character death happens when a player ignores "are you sure?". Everyone's been informed of this ahead of time, and they get a reminder at the critical moment as well. There's always a way out, it's just that oftentimes the way out isn't what that character would do. And then they die. Everyone's been very happy with this system.
The vainglorious paladin won't back down against an enemy they are very clearly failing to handle? That's a character death. The player knew and accepted it. She didn't want her character to die, but she couldn't see a way to justify him running away like the characters who survived did. Now she has a slightly less brave character.
If you quit the table because you lost a character fair and square in a perma or difficult revive campaign you're the problem and no loss... This is a known possibility, grow up and reroll
Eh, it all depends on what the players and GM want. If everyone's okay with death lurking behind every corner then that's cool. If everyone agrees that death only happens in special preplanned scenes that's also cool. There's only a problem if expectations mismatch.
Yes. This mainly happens when everyone has different expectations without realizing it. That's why is important to talk about these things in advance so you don't end up with a GM who thinks it's obvious that PCs can die at any time due any reason and a player who thinks it's obvious that they won't.