So we are, at least in part, talking about using the weapons in the video to kill human beings.
1. The use of lethal violence in self-defense is a morally gray area. We balance the imperative of loving our neighbors (even if they are enemies) against the practical need to make moral compromises as we make our way through a broken world. I do not have an easy answer, and the church has not found a single, easy answer, despite centuries of debate.
Using one of those weapons on a human is pretty far into the morally-dark-grey zone, but I suppose I can allow that a reasonable person might sometimes make that choice, especially since:
2. We live in a multicultural, multi-religious society, where I live alongside people whose religious and philosophical beliefs are different from mine. I can't expect my neighbors to be Quakers.
This brings us to the civil society point:
3. Regardless of our religions and philosophies, here in the US we need to reduce the danger posed by widespread gun ownership. Truly, I don't know what the best remedy is. Options I've see suggested are: arm everyone; arm no one; require strict licensing and screening; or restrict the weapons that can be sold. I'd like to see more data, a better analysis of what works and doesn't work, empirically, to reduce violence. Until we understand better what make a gun owner cross the line from shooting targets to shooting humans, I don't think we really know what we're screening for.
I'll conclude with a couple of positive points I've seen from the gun owners in this discussion:
4. If you must own a gun, then (as
@Tuur observed) thorough training and excellent discipline make a big difference, especially in reducing accidental injuries.
5. Returning to the OP, I agree that some of our gun laws are clumsily written. Evidence-based legislation (perhaps written by knowledgeable gun owners themselves?) would be better.