Because there has still been nothing shown which gives the McMichaels any justification for pursuing Arbery through the streets and then killing him.
That's your pro-dirt-bag interpretation of what happened. The pro-law-and-order interpretation is that two armed members of the neighborhood watch pursued a suspected burglar (suspected for very good reason) with the intention of keeping him there till the cops arrived, who had already been called. The suspected burglar (Arbery) went for one of their guns. A struggle ensued over the weapon (at this point the burglary suspect is considered, in the law, to be armed), whereupon the gun was fired into the attacker (Arbery), killing him.
