In a game where death is not permanent, stealing becomes the biggest crime. If someone steals your life, you can get another one (although it might be an expensive process). If someone steals your 'Ancient artifact of lores unseen', you have to steal it back, otherwise you lose it forever. If the item stolen from you is an expensive consumable and the thief uses it, you're out of luck.
Of course, in real life, the punishment for death wouldn't change. Death is very painful (in lots of cases) and it could scar someone for the rest of their lives. While death is still an illegal act in most places, it doesn't hold the taboo that roleplaying or doing other subjects does. Thus you get the whole issue of murder being more acceptable than swearing, since murder is a part of the game.
While murder is treated lightly in lots of games and rpgs today, I don't necessarily think that's a good thing. We're teaching kids that it's more acceptable to commit murder than it is to be politically incorrect.
MD can change this, but only if people are willing. If there are no consequences to murder, the players can make some. Players can agree to not speak to, trade with, sponsor the quests of, etc., of someone who has hired someone to commit murder or has murdered someone themselves. Lands can choose to banish people who commit murder against anyone, or they can choose to banish people who commit murder against certain people.
People might cry foul for someone being punished by others because of the role that they chose, but that's just stupid. If you choose to murder someone as a part of your role, others can choose to not talk with murderers as a part of their role. Or, they can choose to worship murderers if they want. It's their choice.
The only cases where this fails is when someone doesn't care about trading, socially interacting with people, doing quests, etc. These cases will be rare though, and if it's possible for a player to not care about such punishments, it's equally possible for a character to not care, and people will just have to deal with it.