I'm with you here, but I think it's key to be able to assess whether the holder of that gun is really a threat. Sure take control but putting them down because they have a gun, is a very swift escalation of events, you've not given any chance at all for them to volunterily put their gun down. Stay focused and any advancement from them sure. Do what you have to, but there are clear rules of engagement, those should apply in civvie street too.