Wrong again. Do yourself a favor, break down those 30,000 in categories. That number has been thrown around heavily by the anti gun crowd. Break them down into categories (or continue searching) and you'll find far less than that number are unjustified murders.
Also, are you assuming the 20 million legal owners are the ones committing these crimes? I'm a legal owner, I have what I do for fun and defense, against the illegal owners, who don't obey laws anyway and would not be affected by more gun laws like the legal owners would be. How successful has it been when marijuana, heroine, meth, cocaine, opium etc.. was illegal in all states? The majority of it still shipped to the states despite it's illegal status. The drug war, as more and more people are realizing has only made it easier to get and put the control and distribution of it in the black market. Why would guns be any different? It would essentially be still available and easier to get if banned outright, all while restricting law abiding citizens from sport, hobby and self defense.
Look at the state of Vermont, you just need a drivers license to buy a gun. 16 year olds can conceal carry, no permit needed for anyone who isn't prohibited (FPP). Correct me if I'm wrong, but it's one of the safest places in the U.S., look at major cities in Arizona or Texas, where gun laws are fairly lax. Now look at Major cities in New York or Illinios where they are or were virtually banned. The difference is that crime is much easier to commit when the victim is less likely to be armed.
Despite all that, even if all that were wrong, I stress the protection from our own and other governments being the true reason for the second amendment. And I repeat Thomas Jefferson quote, I would rather be exposed to the inconveniences attending too much liberty than to those attending too small a degree of it.