Lanefan
Victoria Rules
Even the most co-operative of parties would split apart if the situation told them to:You can play how you like, but understand that your table is in the minority, most gamers prefer a different style where players are responsible for playing their characters in a way that keeps the party together.
You're the sneak, we're clanky metalheads, so you scout ahead while we wait here. <DM pulls player of scout PC aside to play out the scouting without others knowledge or interference>
We need to keep watch on the guildhouse but also check the library archives for ownership records; so you two hit the library while we stand watch here. <DM plays through one group first, then the other>
And so on.
I see your underlying point, however, is that players are expected to play their PCs as meta-trustworthy in the eyes of the other PCs. I don't buy into this at all, as I quite like the trope of the spy or turncoat or thief; or of parties whose PCs are operating with different (and sometimes opposing) goals in mind.