I don't believe that anyone in fear for their life would open the door, so that piece of info will be key in how I see this case. Did this man open the door without calling police? Why?
Some people do open the door with a loaded gun and expect that they'll just be able to use it if needed, but if I were on a jury I would remember that they didn't have to open it. I consider whether attempts were made to de-escalate the situation or wait for the proper authorities.
I don't have any problem at all with guns to protect someone inside their own home, btw. I do hold gun owners (including myself) to a high standard of responsibility. It is a HUGE responsibility to be a gun owner, imho.
I don't think someone trying the door handle would be enough to shoot, either. Except in a very few circumstances, like someone screaming that they are going to kill you, I don't think you should ever shoot someone you can't see.
I had a group of drunk kids try my door suddenly and come on in one night myself! It really scared me at first, and I was actually angry with them for that. I'm incredibly glad that I wouldn't have shot them, though. They were just stupid college kids who had the wrong apartment.