Basically, characters (or at least characters the narrative is trying to sell as heroes) should never beg, plead, whine, or even request virtue from others, friends or enemies. They should demand it. So when a character gleefully suggests an innocent person be murdered for whatever silly reason, the response should not be to whimper "Please look into your heart. Is this the right thing to do?" It should be getting in their face and telling them that's not going to happen and making sure they know that sort of attitude is unacceptable and will be punished.
Mass Effect has thankfully done a very good job of this overall. The biggest failing was with Javik.