The father made a statement to the police that they were shouting at Arbery. Did the father make a false statement to police? (That is "proof" that they were shouting at Arbery)
Running at him does not prove that he doesn't fear the gun. If someone pulls a gun on you and you pull your weapon and shoot him is that proof that you didn't fear the gun or proof that you did fear the gun and wanted to use force to ensure you were not shot? Are you saying that Arbery knew when he was 100 feet away that McMichael had a gun? In the video, was the gun visible when Arbery was running up to the truck or was it only visible after McMichael stepped out of the truck with it in his hands? It appears that he wouldn't have been able to see the shotgun until he was beside the truck, which is when he launched himself at McMichael. Is having a gun in your hands going to de-escalate a situation, or make the person without a gun believe they must act quickly to prevent themselves being shot?
That is pure conjecture. Maybe he had apprehension about the man who had been chasing him, exited his vehicle, and approached him with a gun.
If you assault a person, you cannot use that persons reaction to your assault as justification for violence. If McMichael has "stood his ground" at his house, there would not be an issue. If McMichael had "stood his ground" at the house under construction while Arbery ran away, there would not be an issue. From the statements made by his father to the police, they were actively chasing Arbery. Another person had turned him back, and they moved into a position to cut him off. They were not "standing their ground", they were actively pursuing.
You have disputed me by saying that in Georgia pointing a gun at someone is only a misdemeanor and that it is only a felony if you shoot them. That is a misunderstanding of how the law works. Under the assault law in Georgia it is actually a felony to display a weapon during an altercation. It is extremely apparent in this case the the younger McMichael did do that. Arbery died as a result, which under Georgia statute is murder.
You have claimed there are several justification defenses for those actions. Self defense is expressly unavailable to someone who commits assault. Since McMichael did in fact commit assault from a strict reading of the statute, he cannot use self defense as his defense.
You have claimed that they were making a citizen's arrest, but you have failed to support that claim with any available facts. Maybe they saw him snatch a purse and were pursuing because of that. I haven't seen that claimed anywhere. What crime did they witness? Also, as I have stated, under rulings in Georgia just believing you witnessed a crime isn't good enough. A crime has to be committed. In Georgia, trespass requires a) damage to the property b) notification from the owner not to be on the property or c) a request from the owner to leave the property. It isn't clear that he even committed trespass on that day. Ohh, there is an unverified screenshot from a video that shows a blur that might be a hammer isn't good enough. There have been a string of robberies in the neighborhood isn't good enough. The McMichaels had to have witnessed a crime in progress and react immediately to that crime. What crime are you proposing that they immediately witnessed, and where is your evidence of them witnessing said crime?