Adding on to @salem-v post about the non existent “no kill rule” I like to think each team has a designated person they look to for reassurance as to whether lethal force is required or not.
For Team Shadow Gear it’s Jet, he’s more likely to run circles around an opponent to tire them out so if he stands his ground and fights them that means they gotta go.
For the Thunder God Tribe it’s Bickslow, even though he’s a vindictive, sometimes sadistic person his ability to see souls means his discernment is off the charts, he is not the type to resort to lethal means without reason.
For Team Natsu it bounces between Happy and Gray. Lucy used to be included but as the series progress she picks up Natsu and Erza’s particular brand of insanity. Happy, usually being far removed from fights has a more open perspective on an opponent, his analysis skills almost never fail. Gray on the other hand is not overtly vindictive, even if murder becomes a needed option it will not become his last option until he announces it as such, meaning he truly does not think there can be any other option.
For the dragon slayers it’s Cobra, his ability to hear thoughts gives him the most tools to make the decision and as a lacrima only dragon slayer he is less affected by the, sometimes irrational, instincts of the other dragon slayers.
Of course they are all able to make the decision on their own and usually they will however when on a team having one person to look to for such a permanent act does help when in tense situations that can cloud the minds judgement. (As established a perceived slight against a guild mate could result in the loss of the antagonists life)
