Bad guys with guns is a bigger problem than "good guys" with guns, no?
And, yes, most of those guns are obtained illegally, just like street drugs.
And the war against gun smuggling will be just as successful as the war against drugs. In both cases, as long as people want them, they'll get them, no matter what the law is.
The key is the culture, and you can't change that by passing more laws. We know that because it's been repeated tried, and it repeatedly fails. We need to quit doing what has never worked, no?