Probably. Thats fine.
I think you got that in reverse. Why would you want to isolate your players? Its a cooperative game is it not?
Character = player. If the character is isolated then so should the player be.
I think you got this all wrong. The entire group gets to participate in the thinking process, but its the active player that decides what action they are going to take. They are free to listen to, or ignore the advice of their fellow players.
Or, in the case of a quieter or more reticent player, just get told what to do.
It is the exact opposite of inconsiderate table manners. The players and I have an understanding that whenever their characters are not present, they can still be involved with the events in the story as an audience. They can comment, they can offer advice. This draws everyone into the experience, regardless of whether their character is present or not.
What that tells me is that, in effect, all the players are playing all the characters as a unit...the best analogy I can think of is a videogame-style adventuring party but instead of one player running it you have 4 or 5.
What happens if someone wants to make a bad decision? Do they have to argue their way through the peanut gallery first?
I think you underestimate how positive this can work, due to never having tried it this way.
I've had to DM the fights it's caused.
I have to assume you've got a group of players who are all vaguely equal in their willingness to speak up - nobody is dominant, and nobody is unduly quiet. That's a rare group.
And that is boring. This is exactly the thing that makes players turn to their phone.
Look at it this way: You can demand that they wait patiently and silently for their turn, or alternatively, you can involve them in everything, regardless of whether they are present or not. Which of these two sounds more fun for them?
Your way, for them; my way, for the active player. And as the active player is the one actually doing something that player's voice is the only one I want to hear. My goal is to keep what's happening entertaining enough that the other players remain (quietly) engaged.
An example, of a sort: I showed up for last weekend's session of the game I play in with a dead character. She'd died late in the previous session; I knew a revival attempt was coming but didn't know how long (real time) it would be before it happened. As it turned out the party did all sorts of things before reviving me, and I got 2.5 hours of grand entertainment watching them do it before I was - with difficulty - revived. Knowing it wasn't my place to get involved, I remained quiet - other than a few wry observational notes passed to the DM during gaps.
This is bizarre to me. Why would one player offering advice to another player, be a jerk?
Because the advice is either unwelcome (often the case in my experience and always the case if I'm the active player) or unwarranted (the character has no way in game of conveying said advice).
Why? You don't need to play this way. I know this is how a lot of people seem to expect D&D to be played, but personally I think its nonsense, and I reject this style of playing. Your players do not have to play like they are on an island. Involve the whole group in whatever transpires. Allow them to discuss strategies and ideas, like they would during any boardgame, and the game becomes so much more involved and fun.
Well, it's not a boardgame, for one thing. And while you might think this style of play is nonsense a great many do not; and were I to find myself playing at such a table I'd be having harsh words with anyone trying to make suggestions when their character isn't in position to do so.
You should really try it first before you pass judgement on this style of playing. You seem very eager to throw out this idea, just because you seem to think the other way is the way the game MUST be played.
I've learned the hard way that this is how the game...maybe "must" is too strong a word, but certainly ought to...be played. Your way just leads to quieter players being marginalized and-or told what to do, even in situations when the spotlight should be on them alone; and also leads to characters/players knowing things they shouldn't e.g. the anagram-name example.
Lanefan