Looks like most of the basic relationship stuff has been covered, so I'll just add two arguing points that have worked for me when family members have attacked me for owning firearms. On one occasion, my brother started in on me by insisting that "first...", I had to put trigger locks on my guns. I responded by telling him that I don't need trigger locks, they're crap, many are easily defeated, and don't prevent a round from being chambered. When he was about to open his mouth again, I continued to explain that is why I use action locks when the guns are stored. He realizes he's beyond his depth and off the mark as far as his assumptions about my regard for safety, end of conversation.
That was a lucky break, but almost without fail, I've been able to let someone get wound up about the guns, what if the kid ever got hold of them etc. I let it go with some flipant remarks about how they're locked up and it's no big deal, then when their energy level jumps up a notch, I lay into them with the fact that it's not the guns I'm worried about, it's the ammo! I could give my kid my shotgun and a pipe clamp, and she'd be at equal risk of getting an injury from either, but the ammo, the ammo is what I'm worried about! Again, realization they don't know what they're talking about, conversation over, doesn't tend to come back up.