I haven't really played MD much, nor experienced the thing about killing that people have been talking about, so I don't suppose I can really give a qualified comment, but I think the thing about death in real life is that it takes away real life. When you die in real life you die, and your experience is over, and everything you have gained and hold on to and value and is important to you is taken away. You lose everything, and that's just for your effects on you. Everyone who is dear to you loses everything that depends on you, too. And so in society we have rules to make sure that no one can go around doing this to any person and all those around them without a really really really good reason that most can agree with or at least justify. But in MD it sounds like death and murder doesn't have the same thing at all. It doesn't sound like you lose all your possessions (well, maybe you do, but if you come back you have a chance to get them back?), all you stand for, your family, your identity, your people, all you treasure and all that is important to you. Instead, from what I'm getting from Mur, death here is simply part of the experience, a different part of experience. That is, death here is part of the gameplay, and thus by definition part of life here, since life is basically the sum of our experience. It just happens to be called the same name as the 'death' that we are familiar with (or rather, think we are familiar with) in real life. Or at least you can think of it that way, at that level (at the level where we are all shards of the One, welll, that is sort of different but ehhh)
I guess the important thing is to recognise the reasons for morality and law and order, and what is behind them. There are reasons why morality is thus in RL, there are reasons why law and order is thus in RL, and there are reasons why they are so in MD, and there's the reality behind those reasons. Without that we will always be conflating the morality here with the morality there, which will perhaps tend to make us angry about people not respecting life and respecting death, or appearing to condone murder, or not treating them with enough importance, things like that. Looking at them separately, perhaps we can understand better how killing, murder, and death is thus here instead. I guess.
That's just how I see it, anyways. Hope this helps in some or any way.