Uhm. Why should it only happen in Evil campaigns? What I'm talking about is something that's pretty much an every day occurrence - both in a medieval society and in modern times. Someone doesn't pull their weight, they get fired. In medieval times, that means the serf gets his ass beaten for not working hard enough, or the peasant's family dies if he doesn't do enough work on the farm and grow enough food. In modern times, it means your ass gets booted out the door with severance pay.
I shan't & can't
argue with the principles that it wouldn't happen unless you're metagaming, you're correct. But you didn't get fired in medieval times, you could be punished or even killed (rare), but the bonds of hierachic duty didn't work that way, there is no quit option. Much less with 'theoretically' equal in status party members.
But D&D isn't medieval fantasy for just that reason, at higher levels theres no society that has rules for individuals being in charge of Absolute Power
TM. Falling back on human nature, haven't you ever had 'fail' friends that you had to keep helping, but you did so anyway?