Short answer: Ask yourself "Does this person need to be shot."
The long version is does this person have.
"The intent to cause great bodily harm, or kill someone."
"The ability to cause great bodily harm, or death."
"Access to cause great bodily harm, or death."
To further define the above..... Does this person intend to harm or kill someone, and possess the ability to do so, while in close enough proximity to do so.
a 5 year old who really wants to kill you for doing something to his mom, that's not armed with a weapon does not have the ability.... Bad shoot.
Someone calling you on the phone saying, I'm coming to your house in 30min with a shotgun to kill you and your family for firing me.... Doesn't have access. (at least yet, and if you wait around for him you're a fool.)
An unknown twenty something year old adult, in your home, in the dark of night, unannounced... Certainly has access. Likely has the ability. When confronted says something about "Dude man, JoBob said it was cool to crash on your sofa man..."...... Doesn't have intent, and is likely just drunk and confused.... (bad shoot most likely)
Someone shooting your dog, on your property, might have actually believed the dog met all three criteria, and reacted, possibly poorly.... you reacting in kind is almost certain to land you behind bars.
The long version is does this person have.
"The intent to cause great bodily harm, or kill someone."
"The ability to cause great bodily harm, or death."
"Access to cause great bodily harm, or death."
To further define the above..... Does this person intend to harm or kill someone, and possess the ability to do so, while in close enough proximity to do so.
a 5 year old who really wants to kill you for doing something to his mom, that's not armed with a weapon does not have the ability.... Bad shoot.
Someone calling you on the phone saying, I'm coming to your house in 30min with a shotgun to kill you and your family for firing me.... Doesn't have access. (at least yet, and if you wait around for him you're a fool.)
An unknown twenty something year old adult, in your home, in the dark of night, unannounced... Certainly has access. Likely has the ability. When confronted says something about "Dude man, JoBob said it was cool to crash on your sofa man..."...... Doesn't have intent, and is likely just drunk and confused.... (bad shoot most likely)
Someone shooting your dog, on your property, might have actually believed the dog met all three criteria, and reacted, possibly poorly.... you reacting in kind is almost certain to land you behind bars.