“If only someone else had been carrying......”
Or a handgun in a quick-access lockbox, it may have cut the toll down to three.
People generally don’t carry at parties, though I’ve been Designated Driver with a hot one in a holster a time or two, and known of other DD’s who have carried, but mostly for dealing with the street outside the party.
I don't know where you get your information, but people who carry usually carry all the time. At home, at church, all day long and all evening. These are the people who be useful to society. Someone who carries only part of the time just isn't going to be ready when a situation arises.