I am fanatical about people not pointing loaded spearguns at me; it happens most often underwater when people become distracted. I am very careful how I swing my loaded gun around underwater and to be honest, there are times when the gun may get inadvertantly swung past another diver, especially if I am unaware of where the other diver is located. This is a very rare occasion and usually involves a diver swimming in front of my gun more than me swinging it past them.
I do not put my finger into the trigger guard until I see, or expect to see, my target.
However, with regard to a rubber powered speargun, it is not difficult to tell for sure whether it is loaded or not. So people often will handle an unloaded speargun on a boat or in a shop MUCH differently than they would a LOADED speargun; I know I do. I might pick a gun up off the deck and spin it around and make very litle consideration about someone who is 10 or 20 feet away. If I were handling a loaded gun, I will be aware of EXACTLY where the gun is pointing all the time. It becomes second nature.
In many regards, a speargun is MORE dangerous than a hand gun because a hand gun will not fire by iteself. A loaded speargun can fire at ANY time with no warning. The spear and trigger are under tremendous stress and if the shaft is not locked into the trigger perfectly or should the shaft and or trigger become too worn, damaged, corroded, or cloged with sand/silt the gun might just fire by itself. I've seen spearguns mis-fire a number of times. They are scary.
Carelessly pointing of an unloaded speargun at someone 15 feet away is probably not a safety issue, but it would certainly make me nervous.