That is a black and white view on a gray topic. What I mean is the GM does effect and control almost everything. At the same time a GMs job is to ALLOW the player to do something to kill himself. But your point is the same as Lanefan's that a GMs power to interfere and control everything doesn't mean he should, also never means he can't. So in a case of player vs player combat if GM intervenes he is stopping free will and invading on the choices of the players. At the same time he could have a guard run into the middle of the fight and get shot... that would not be. What I am talking about is that if a group is going to TPK because events the GM controls its his fault. If he allows one party member to die based on his decisions and dice roles that one thing but a TPK pretty much means the GM went too far unless all the players decided to jump of a cliff. If for some reason they thought they were going to get a free wish if they jumped the GM should add some saves or something so hopefully at least one player lives. ...A thought the story of the time the party all died trying to make a wish would likely not be one they forgot.
I agree strongly with this.
The DM is in charge of what the players
could do.
The players are in charge of what they
choose to do.
But in order to make a meaningful decision on the subject the players have to have a rough idea of the possible outcome.
Lets say the players are trapped in a featureless room. There are 4 levers in this room.
From this information, the players cannot make any meaningful decisions. They have no idea what outcome of pulling any lever
could be. The DM is in complete control here. No matter which level the players pick, the DM controls the outcome. Therefore, in this situation, if the players were to pick Lever 1, and they all die, the DM is completely at fault here. Insufficient information was communicated to the players on the possible outcomes of pulling a lever. The players could choose not to play the game ie: sit still and do nothing until they die, or they could essentially let the DM choose their fate.
Lets look at another situation: The players have been exploring the Cube. A series of featureless rooms with levers. Each of the levers is color coded. Red, Blue, Green, and White. The players have pulled enough levers to find that Red has a 90% of Bad Things. Blue has a 50% chance of Random Monsters, Green has a 25% chance of healing the whole party to full, and White always opens a door to another featureless room. All of the levers have at least
once opened a door to a new color-matching room.
Here, the players have agency over their decision. The DM has pre-defined what each lever may do, and the players have a reasonable expectation of what potential outcomes they may experience. In this situation, if the players pick the Red Lever and die, they understood that was a possible outcome. If the players pick the Blue Lever and are attacked by monsters, they knew that was a potential outcome. Therefore, it is their fault they died.
If for example, the players pulled the Green Lever and they were attacked by monsters, or pulled the White Lever and were instantly killed, the DM would have denied the agency he had granted the players and would once again be at fault for their death.
But more realistically, what usually happens is the party is wandering through The Woodlands and encounters Dangerous Monsters. The choice to engage the Dangerous Monsters may be on the players, Player 1: "Hey! Lets go kill the monster!", who hasn't heard players say that?. The choice to engage the Dangerous Monsters may be on the DM. DM: "They wandering dragon spots you and takes exception to your haircut." Player 2: "But, I'm wearing a helmet?" DM: "Exacty." Often, it's a mix (players failing sneak checks, random rolls to determine the monsters disposition, etc...). Once combat is engaged everyone rolls to see how they do, and there is a known possibility of death if things go poorly for the party or well for the monster. There is some degree of agency upon the players here and some degree of angey on the DM to determine the endgame. Like most of D&D, the outcome is cooperative. The DM may be responsible for placing a too-dangerous encounter, the players may be responsible for playing dumb (the most common cause of TPK's IMO).
As long as players are able to make a meaningful decision, they have agency and therefore share some of the responsibility. If the players are denied agency, then they likewise are freed from responsibility.