Krellin, maybe (I say maybe) the question is whether something is DESIGNED to harm others or not.
Alcohol? You don't harm others if you drink, unless you drive while drunk or use something dangerous.
In fact, if you drive, you can't drink (at least I hope that there is such law in the US). It's not the alcohol you ban, but the situations in which alcohol is dangerous.
But gun? Since a gun is ALWAYS dangerous, can you say "Well, you can buy it but only to use without risk for others"?
Sure you can use guns to - erm.. - hammer a nail into the wall? Well, sure, but... there are hammers for it...
Legally owned? Oh, well, if that gun shooting me is legally owned, I suppose it's ok...
(but maybe, if you didn't have that gun, I'd feel safer!)