Update

Passworded games
I cannot enforce creating passworded games as a rule, as once a game begins it doesn't say if it had a password or not.
However, I do not see a problem in random people joining the campaign "by mistake" since they don't need any special requisite or to fly in a special way to play with us in the campaign game.
However if you prefer to use a password and play only with other people who are playing for the campaign, that's fine