Imagine you are hunting on Federal, state, or county land. You think you know where the boundaries are, but without precise GPS knowledge, you can't be sure. Suddenly, somebody challenges you claiming that you are trespassing. You start to protest, but blam! You're dead.
Your killer was right that you were trespassing, you were carrying a loaded gun, and so he claimed self-defense.
What if you're walking on the road and pass somebody's property. For whatever reason the person shoots you. Your killer claims self-defense. You were carrying a gun and there are no witnesses.
These kinds of shootings have occurred. There was a case in Wisconsin a few years ago where a group challenged a hunter because they believed he was trespassing. He shot and killed at least five of them. He did claim self-defense, but the survivors claimed otherwise. I believe that hunter is in jail.
But if there are no witnesses and no survivors, who is going to prove that the shooting was not in self-defense?
The "shoot first" laws make it a bit unwise to enjoy the solitude of hunting alone.