just a personal opinion, but to me it looks like one of two things.
noretoc said:
a - this is a test of your loyalty to your friend and party members, and if you take the ring, it will probably turn out bad in the end.
Or, at the very least, YOU (the character) will turn out "bad' (evil). I mean, it's pretty clearly a trap/moral delimma set up there. Classic. It could be fun to play either way. You (both player and character) are probably 'better off' not accepting it... but it could make for some interesting role-play if you did. However I suspect (and from further reading it looks like I was right) that there will be an alternate reward that's just as good if you don't take the artifact (especially considering there could be any number of negative consequenses!)
noretoc said:
b - Your DM is a cad and you need to find another. Setting up situation where one player can have fun by making it less fun for another player is not a good way to run a game. Not even a average way to run. It is a BAD game.
Well. Possibly. But not necessarily. I mean the GM's a cad if he wouldn't do something to compensate the other player for his loss assuming the character who was asked to kill went ahead and did it. You've *always* got to plan for the eventuality of what if a player does something horrible. But it's very character defining to make the character DO, choose, be. That's a large part of what the game is all about IMO. Evil artifacts or creatures demanding the sacrifice of something near and dear is practically fantasy canon! NOT doing it would be evil on the GM's part!