Coming from a perspective of one who has had no previous RP experience with any of the players here, and who has no experiential knowledge of the situation that prompted this thread - here is my outsiders view.
In my 30 plus years of playing RPG's my experience has been that the groups where the players understood and respected the IC/Ooc divide were the best ones.
E.G., two players, one playing a thief and another playing an honest party leader could discuss how thiefy boy had or would do something vile and secret but IC the honest character would know nothing about this and could not act as if influenced by his OOC knowledge without an IC reason or experience that had tipped him off.
Or two players could plot any kind of scheme OOC, but unless they explicitly stated 'ok, out chars talked about this here and then', or actually RP'd it then they could not later have claimed to have done so.
If this divide were to be violated then that would be regarded as cheating and if it continued then the player would no longer be invited to play with the group.
As a player I found the groups always ran better and were less stressful and more immersive if the other players understood this and the DM enforced it.
As a DM I always made this clear and things ran better because of this.
However.... I had enormous difficulty finding any kind of on-line group with the same appreciation - for some reason the line has always been very much more blurred and RP just seems to fall apart because of this.
EVE is now the only RPG I play, and I only still play it because I can just, IC, assume that anyone who makes any reference to OOC stuff outside OOC channels is just insane. Thus is my immersion maintained.
Ideally OOC is totally free and people should be able to plan provisional plots, express things thier chars might do, and well anything, without any fear of someone taking that IC.
The reality is that different people come to EVE with very different views on what constitutes acceptable behaviour, definitions of terms, general play, and so on.
I just try to learn how to play with the people I meet as I go along, aware of the dangers of my preconceptions of others.
I definately find that it pays to never speak OOC in chat unless I prefix it with OOC/ or something and if later someone is saying my char said or intended this or that I could say, "You are either mistaken, or you are, basically, cheating by using OOC info to enhance the knowledge of one of your chars"
I guess this is one reason why I am in a two man corp where both the people are me....