hy would anyone assume these criminal gunmen, who shot the cops, got these guns legally?
Why would anyone think that, if guns were outlawed for citizens, that events like this would not happen? The Boston Bombers used a pressure cooker. Should we ban pressure cookers?
Well, some countries are getting nuclear weapons. Should we just throw our hands up and say, Oh well, North Korea can get them, so anybody can, let's just give up, because we aren't going to win?
An extreme example, but just following your logic. There is no reason for any private citizen to have high capacity weapons. End. Of. Story. We could have banned them years ago and greatly reduced the number now floating around, but some people don't see the difference between gun control and gun bans and fight even common sense gun legislation. As long as we have a powerful gun lobby and a congress that refuses to act, we will keep getting what we are getting. That you will never get rid of them all is a red herring, you can and will get rid of a lot of them and make them much harder to obtain.