I think one of the biggest causes of violence is when a criminal boards a boat looking to steal, makes it into the cabin and surprises the sleeping owners. Maybe the criminal thought the boat was unoccupied, who knows. But once inside and someone wakes, all h&ll can break loose. With guns involved, bad things can happen.
Once I was tied up to a dock in SC, and left the salon door open as weather was nice. I was boarded in the middle of the night. By a raccoon!!! I woke with an adrenaline rush, scared the beast who then was bouncing off the walls, that boosted my adrenaline further. Lights were out and I had no idea what was going on until the critter had already exited the boat. If I had a gun in my hand, who knows what would have happened.
I do keep guns on the boat, but am well aware that they are of very limited use, and also that they do pose a real risk. A good argument can be made to both carry and to not carry. I am close to being on the fence. A little to the carry side, though.
For some element of safety, I keep the guns in one locker and ammo in another distant drawer.