The "spontaneous farmer hate" comes very, very near to a straw-man example, of course. But I can tell you the sequence of events that would occur if a DM made a "woe is me, my player hates farmers, my players suck" post here. In sequence:
1) Lots of people: "your players suck! the lot of a DM is hard".
2) Several people: "the situation you describe doesn't make any sense, clarifications please".
3) After some teeth pulling: "well, yeah, the campaign was advertised as a social-intrigue campaign*, and the character in question is a tricked out social-monster with minimal combat abilities whose ambitions are purely political".
4) Lots of people: "DM-sir, dude, the problem is your fault".
Er... no offense, but I don't think that's a correct interpretation of a straw man argument. It was an example given of the sort of play where I've seen this type of situation come up. A straw man would be more like, say, involve taking my example and then responding to a different situation that you yourself come up with. Such as, perhaps, a situation where a DM misled a character as to the type of campaign, as opposed to a situation where a character spontaneously invented a personality trait that ended up disruptive to the campaign.
Seriously though, I think your point breaks down when you say that "if a player is being completely honest with their character," then the DM is at fault.
Do you really think it so impossible for a character to have elements in the backstory with ramifications that the DM doesn't forsee? Or for a player to genuinely decide, in the middle of the game, that he has a new personality trait? Or that his interpretation of a previous personality trait is different from the DMs?
I don't think these are common situations, sure. But I've seen players that have acted like this. Sometimes to intentionally be a jerk, more often because they just don't quite get what is wrong with a character being disruptive and causing conflicty. It is this sort of thing that I am talking about, and I think a very different situation from a DM advertising one type of campaign and running a different one.
Thirdly, the player that is balking may actually be disruptive. Either he is mistaking his own in character stance for an out of character stance (because my character wouldn't want to do this, I don't want to either), or he's letting his out of character feelings influence his in character stance (I don't want to take this plot hook, but I don't want to look overtly like a jerk, so I'll throw an in character fit), or he's actually the sort of player that gets a kick out of derailing the game so as to remain the center of attention at all times.
This is really the situation I'm referring to. Honestly, with most players, when you have conflict between a character's motivations and the direction of the plot (or even just the direction other PCs want to go in), that sort of conflict can be an
opportunity more than a disruption. Some of the strongest RP and character development I've seen has come out of mature players having that sort of conflict - and either making the hard decisions (that might result in a character leaving the group) or finding a way to resolve it.
I think your point about the player merging character and player positions is a key one - for a good player, they can often resolve an in-character conflict with an outcome that the
player finds interesting even if the
character is upset with it. But for some players, they can't break out of that divide, and that is where this sort of problem comes from.
If this turns out to be what is going on, we probably have a blown session, and it's the DMs job to privately take that player aside after the session and try to explain to the player that he's not the only one playing the game and that therefore he needs to keep in mind that he has a responcibility to everyone else in the group to play in a cooperative manner. That doesn't mean he has to betray his character concept, but it does mean that he has to be looking for ways to make his character work with everyone else and if he can't, then he either needs a new character or a new group.
And I guess this is where the real difference of opinion comes from. If this sort of thing happened, I wouldn't just call the session. I'd try and have that conversation right there, possibly with the assistance of the other players. Either finding a good resolution in-character, or try and convince him, as you note, that he needs to try and be 'part of the party'... or, worst case, let his character go off and sulk and let everyone else keep playing.