I recently had a band of Dead Suns PCs go all cold-blooded-killer on some KO'd goons. A few more details in the write-up over here, but I'm curious if any of you GMs out there have had a similar experience. Have you ever seen your Neutral/Good crew of PCs turn into a band of Neutral/Evil killers? Is it ever appropriate for a GM in this kind of situation to say, "Are you sure you want to do that?" Or are morally dubious actions like this always best left to the discretion of the PCs, even when it seems out of character?