Yeah, that's the lesson to take away. Similar to someone breaking into your home. If you shoot him and he dies, the lesson is, don't own a gun.
GZ's gun may have just saved his own life or prevented him from sustaining serious and permanent damage. So no, I don't think the lesson is, he shouldn't have had a gun. The lesson is, it doesn't pay to try to keep your neighborhood safe and look after your fellow neighbors. It should be every man for himself. Oh, and if a black man attacks you, just let him beat on you until he thinks you've had enough. Hopefully he won't kill you or cause permanent bodily damage. Because obviously if you defend yourself, you're a racist, even though the person attacking you is racist.