Couple of possible responses:
1) He's right in a way, although 2A doesn't "come from" that motive, but it is a guarantee of the right to self-defense against any and all. Slave revolts were always a worry and the native Indians (feather, not dot) were as loving and kumbayah with the Colonists as they were with other tribes -- as in, not so much.
2) Playing off #1, his reason is why 2A is still vitally important. The "slaves" are more open about wanting to kill Whitey and some of the "natives" (the Left) are no less eliminationist in their rhetoric and actions.
In the interest of watching Glover's head explode, I'd like to riff off #2 by telling him, "so, yeah, bud; your Black brothers are a bigger problem in terms of hatred and violence than ever".