The answer to your question is that you probably can't change their minds. And, frankly, you don't have any right to do so. Your parents should be respecting your wishes where guns are concerned, but that door swings both ways. You, too, should be respecting how they feel.
Now, I say that they should be respecting your wishes, but that's a bold statement without knowing what your wishes are. You are doing something I've always fought against. You are making a life-changing decision based solely on emotion. Knowing this, I can infer that you're probably asking for some pretty big changes. The way you talk about your family, it sounds like they're a guns-blazin' southern family who hunts, target shoots, etc. all the time. BUT, again, I can't trust your emotionalism to accurately represent the picture. If your family enjoys hunting or target shooting, then let them. Nobody says you have to be involved! You don't feel comfortable picking up a gun? Then don't pick up a fucking gun, genius! Your feelings on this matter don't get to dictate how others behave.
Now, with the advice out of the way, your letter gives me a perfect opportunity to talk to the many other people out there who feel like you. A LOT of people who didn't care about the whole "gun control" issue are now siding with the anti-gun folks because of the tragedy at Sandy Hook.
Let me explain to you what happened at Sandy Hook, because I don't think you (and a lot of others) really get it. An insane person walked into a school and murdered people. That's it. That's what happened. He was insane and, because he was insane, there isn't a reason for this. The fact that someone does something idiotic for no reason is practically the definition of insanity.
Human beings are not comfortable with that. We demand to know a reason! I'm sorry, but there ISN'T one. Guns didn't do this. Video games didn't do this. One crazy psychopathic motherfucker did this. ONE human being. Frankly, shifting the blame to all these other things diminishes what really happened there.
Guns aren't getting banned. It just isn't going to happen, no matter how much shit Obama talks. It would take a Constitutional Amendment to do so and that'll never happen in either of our lifetimes. So you and every other anti-gun person had better just suck it up and get over it.
But what would happen if we did ban guns? Stabbing sprees, that's what. See, the problem isn't the weapon, it's the species. Human beings are an inately violent and vicious species. In fact, we were FAR more violent back when we didn't have any weapons at all! Before cavemen even learned how to sharpen a stick, we were beating each other over the head and killing by the dozens. Take all the weapons away and you'll still have just as much violence, because that's part of our culture. I know, it's reduced violence in other cultures (England, Australia, etc.) And those cultures *never* had the gun-nuttiness that we do. Those cultures didn't have gun ownership as a fundamental right guaranteed to them.
Listen, bad things happen with guns. No doubt about it. There are plenty of people who misuse and abuse them. And that's true of any tool that mankind has ever used. But you aren't going to change a man's violent nature by taking away his tools of violence. Do you make it harder for him to act on that violent nature? No, you really don't. The problem is our species' insane bloodlust and that some people can't keep it in check. If you really want to get rid of all the guns, work to create a culture where nobody feels like they need them.
That's a long row to hoe, my friend. Frankly, I'd be happy to see a world where guns aren't needed or wanted anymore, but that is a very very VERY different world than the one we live in now and just snatching the guns away from people will do precisely DICK to change that. You're fighting against 100,000 years of violent human history and instinct. Yeah... good luck with that.
Hating You Eternally,