Good points, Shasta! I think maybe not so much the instability of any family member should be a deciding factor, but if you have an unstable person living in your house, it's probably a good idea to really think about whether you should keep guns at home. But yes, we should stop demonizing responsible gun owners. The vast majority of gun owners will never commit a crime.
Still, it's worth thinking about the fact that many people who become criminals never purchased their guns with such an outcome in mind. In the midst of a very heated argument, when no one is thinking clearly, that is a dangerous time to have a gun within easy reach. Or after a devastating job loss. Anything like that. I imagine most people who kill a spouse, family member, friend, or even acquaintance would take it back if they could.