You can shoot anyone who crosses a door or window frame without permission? No... You have to "believe" the intent was to cause death or great bodily harm.
Agreed. You must have a reasonable belief that you (or another innocent) are in immediate danger of death or grave bodily injury. If someone breaks into your house and is headed out the door with your TV on his shoulder, here in MA you can not shoot him as he leaves. We can argue about whether or not the law should be changed, but the law itself is settled in this respect -- in MA you can not use deadly force to protect property. In MA, you can only use deadly force to protect someone from death or grave bodily injury.
Is someone as so described in my prior post, without a doubt, demonstrating said intent, with an open/shut self-defense out? I'd say yes, but I'm really sure heard other that night.
In self defense, it is my impression that there is little that is open and shut or black and white.
However, if someone has broken into your home, has a knife in their hand, is shouting, and advancing upon you, the fact that they are shouting gibberish does not reduce the threat. The fact that his knife is at his side instead of pointing does not seem to me to be of major consequence. Disturbed persons can be just as dangerous as rational people (perhaps more so). Anyone who has done the Tueller drill knows just how much of a threat someone can be if they have a knife and are within 21 feet of you.
If it was the drunk neighbor who got the wrong house, didn't have a knife in his hand, and was belligerent but not armed, that would be a different matter entirely.
But if someone has broken into your home, is armed with a knife, is shouting unintelligibly, advancing on you, is not obeying your orders to stop and drop the knife, that sure sounds like an immediate threat to me.
I would be very interested to hear the arguments that were made to suggest that deadly force would not be justified in this type of incident. I would be intrigued to hear the instructor's thoughts on this matter.
IANAL, but I have serious questions about the advice you were apparently given.