The ball's still in the players' hands, though to start them.

And once in a while those players have a point.
A point of what ? Of having more power because they think an interpretation of the rules say so ?
You know, as part of my usual DMing style, I don't care, when a player makes a suggestion of that nature (which does not happen that often and which I would hardly called "pushing"), my usual answer (unless it's absolutely outrageous but I don't think that has ever happened in recent years) is "OK, we'll do it your way to save time, as long as you are absolutely sure of your case and we will not come to regret it if we look at it in detail later". About half the time, the player simply drops it.
Yes you are. You're saying I have to play it within a bounded area of ethos, outlook, and actions regardless what the character might otherwise be or do; and that's telling me how to play.
No, I'm telling you that if out of the whole infinite potential area of ethos, outlook, and actions, you cannot refrain yourself from doing things which are contrary to the table's usual way of play, you are indeed not welcome to play with that table. This is a collaborative game, the most collaborative ever, and group arguments always trump individual ones (especially if it's the individual basically asking for a license to act like a jerk).
Out-of-character conflict around the table is bad but in-character conflict within the party is not, and one just has to trust one's players to be wise enough to keep the two separate.
And does this really happen with leaving sequels ? I had three friends (two now) who claimed that they could play that way, always had, but the result is that one of them was kicked twice from our tables, and out of the remaining 2, one has stopped playing in 2 of our current campaigns, and the last one is the ONLY ONE that still creates tension between players with his behaviour (I exceptionally allowed LE for my Avernus campaign, for another guy playing a priest of Tiamat, it's absolutely fine, but the guy playing - again - the assassin is very often at odds with the others, both in and outside of the game.
And these are very mature players. with decades of experience of the game, and really good friends out of the game.
And this alone is a good reason to spin the first few levels out longer than just a session or two each; as it's during these very low levels that the characters in-character can get these conflicts out of their systems and sort out who's welcome in the party and who isn't.
Listen, I have played that way for years, but first it's not true that it sorts things out naturally, conflicts can arise at any time with a new objective in the campaign, we see that all the time even with characters who are reasonably congruent.
Second, the reason we don't play that way is because we unfortunately have just a few hours to play every week (compared to almost every evening when we were playing in a more free form mode). This means that we want to have adventures TOGETHER, including with the DM, and that almost every minute spent scheming against the others is a minute where at least some of the table is not participating.
When you add this to the fact that it always leaves scories on the players when the characters really clash, it's simply not worth it.
The history of the character is part of the campaign, yes; but the future of that character still belongs to its player.
Nope, if the player leaves with his character, the character does not disappear from the campaign, the DM is absolutely free to keep the ACTUAL character (the sheet does not mean anything, the character has only "existed" by being played inside the campaign).
Orwellian groupthink has come to D&D. By this stricture individual thinking is banned. Individual or unilateral in-character action is banned. A character acting on its own agenda is banned. Chaotic PCs might as well be banned.
Huh, no. But it all comes back to Matt Colville's "do not be a wangrod", it's not because you could have a character that is a jerk that you are allowed to.
This type of advice intentionally ignores the fact that an adventuring party is made up of free-thinking individuals. Part of the true joy of D&D is that as your character - as well as your party - you can (try to) do what you want, often without the fetters imposed by real life.
This is not real life, it's a game. It's a collaborative game, that you play as a team, and by doing so you have to accept the rules of the team. It's simple respect. Your freedom stops where it begins to infringe on other's, and your fun HAS TO STOP when it infringes on the fun of others. Simple respect, simple consideration.
If it's done in character it should be sorted out in character; and the players all have to remember that not every character is going to think like theirs do.
And that is absolutely fine, the only thing is that characters do not really exist, they are just figments of a player's imagination, so they are under HIS control, and if the character is acting like a jerk and makes is so that the experience is not OK for another player, than it is simply not OK.
A common example is a party dithering on its tactics planning, which can get boring as hell after the first few minutes for characters (and players) not directly involved - i.e. the non-tacticians of the group. In these cases the sooner someone does something crazy the better, whether its my PC or someone else's.
And it happens at our tables as well, but there is a difference in doing it because the planners have been doing it for a while and should be respectful of the non-tactician too, or whether it's done on purpose, up front, in a purely destroying manner that has no respect for the planners.
it's all a question of balance, and of respect, of the PLAYERS (the characters have nothing to do in there, they are only what the players want them to be).
If the party splits in X directions it's my job as DM to run that many parallel games however I can until-unless they get back together.
And I don't consider it my job. My job is running a game for a reasonably united group of friends adventuring together, which again does not prevent discussion, dissension, even harsh words and fighting, or a bit of splitting, but as long as it stays within the boundaries of everyone having fun, which is not the case when people have to spend the majority of their time waiting for the DM to come back to them because everyone is off doing what they want in their corner.
We has sessions like this, which is why, call it a table rule, we don't do "side intrigues" with the DM going off with one player. We have exceptions of course, but in general everyone witnesses everything.
Especially in these days where it's so easy to zap out of the session on a phone...
Sure; but the same underlying mechanics are being used, right? The barrel example is a simple case of passing one Hide check and failing the next - no problem there as it reflects the reality of the Rogue not being perfect every time.
I thought it was an answer to your point about the players being able to assess the way the world and the rules work.
What I'm talking about are precedent-setting rulings where the DM doesn't adhere to the precedent. An example: say my PC has got hold of an Adamantine Axe whose main property is that is cannot lose its edge no matter what. So, we get to a stone door our Rogue can't open and as my action I declare "I'll try using my axe to chop through it." The DM, who never considered idea this when dreaming up the Axe, thinks about it a moment then says "Well, if you don't mind spending half an hour at it and don't care how much noise you make then yes, you chop through the door" (i.e. makes a ruling and grants auto-success).
Simple fleeting moment in play, right. But wait. With that ruling the DM has just set and locked in a precedent: Adamantine Axes can cut through stone, albeit slowly. Which means I-as-player can now expect - or certainly should be able to expect - this to be a consistent thing going forward and thus can base decisions around this information; and if the next time I meet a similar stone door I'm told I can't cut though it I'm going to both in and out of character be asking why.
In that case, I agree, that kind of WORLD consistency is important, as you can see, the rules matter little here...