What strikes me about this thread is that I think what we are really discussing is intrinsic conflict.
Choosing to create a character that is diametrically opposed to the general thrust of the campaign naturally leads to direct intrinsic conflict with the bulk of the PCs. This would be true if the thrust of the campaign was evil in nature (e.g. most PCs playing a bunch of Nazis doing groundbreaking experiments in living human subjects) and you chose to play a compassionate good person who wants the experiments to end, and the prisoners to be set free.
The reality is that if you play with an agenda that is at odds with the bulk of the player group, and you make decisions that impact the bulk of the player group (which are seen, subjectively, as negative by the majority of that group), then it is axiomatic that many players will be displeased with the outcome.
What is important is whether your contrary character is externally consistent with their hidden agenda. If they have an open agenda (that is, explicitly stated goals of which the other PCs are aware), and succeed, then everyone else had it coming, IMO.
If you keep your agenda hidden to the point that it has no impact on your character at all, then the other PCs will experience a massive cognitive dissonance between the public actions of your character (up to the point of betrayal) and the subsequent betrayal. This will likely result in OOC repercussions as I think may have happened to Mark. Nobody saw it coming, and the reactions were possibly quite acute. As Bryn has identified, you need to inoculate the at rest of the player base by providing an appropriate amount of information, such that - as in a really well-scripted movie twist - those who were paying attention go “Aha ! I knew it !” when your character executes the betrayal. If everyone goes “WTF?” then cognitive dissonance is the next result. In other words, it is about maintaining external consistency relevant to internal agenda.
If effect, the fully hidden agenda strikes at the heart of the larping social contract. We all agree to play be a set of rules, both explicitly (as in the Teonn ruleset) and implicit (as in our larping culture’s expectations of conduct in the shared experience). IMO, the implicit contract requires sufficient information from which the participants (both PCs and crew) are able to draw accurate conclusions about the nature of the environment in which they are collaboratively creating a shared reality. If an agenda is kept hidden then we are not really sharing in the full nature of the reality. Working with the GMs is a good way to develop ways in which your character’s agenda can be publicly expressed.
Even if you have a publicly understood agenda, you may wish to also consider the impact of an adroit execution of that agenda.
For example, Sir Xenith was a Knight of the All. The rules said “All Morhkin must be destroyed”. If I wanted, I could have ganked Morhkin PCs in the first Teonn game. It would have been in keeping with the setting, but I considered the negative impacts, and discarded it as an approach. Instead, I played him hard-out racist against Morhkin and gave them all shit. It created many shared roleplaying moments.
I suppose the thesis is that if you wish to play a character that is diametrically opposed to the majority of the other players, then you need to take extra care to design your character with the implicit contract in mind.