Disruptive for what?
Fighting monsters and looting dungeons? Sure. You know what else is disruptive for that? Traps. Resource scarcity. The monsters themselves. Bluntly, a lot of people are under the misconception that a game being co-operative means there should be no obstacles nor friction to co-operation. That is really, really far from truth. In actual fact, a good chunk of co-operative games add obstacles and restrictions so that co-operation becomes more challenging - because co-operation itself is part of the challenge. There is no inherent flaw to one or more special roles existing to create mayhem in the group. It's a difficulty toggle: there's a choice between games that don't need those roles and co-operation is hence that much easier, and games that do need them and you need to watch your back as a consequence.
---
You are correct about public campaigns & I would have to amend my statement to cover them.
But, consider: typically rules for specific campaign are only added when basic rules DON'T include such rules. And it typically isn't necessary to add rules to ban something no-one ever tries - to the contrary, bans are often targeted at common things. So there are two possibilities:
1) player versus player, under basic rules, is possible and common
2) a lot of campaign holders decides to add a redundant rule for whatever reason.