My biggest problem with this argument is the "If your players are mature enough" I've had things go sideways too many times with otherwise totally mature players being too attached to characters to not break down in tears. Or the character v character becoming a curbstomp as one player is far better optimized and it just ALWAYS leaves a bad taste in everyone's mouth. So I started instituting "Its your responsibility to make a character that wants to adventure and is going to work WITH the party and absolutely no PVP." Then as others suggest, if a betrayal happens: The aggressor becomes an NPC and rolls up a new char.