This isn't a good argument. Criminals get guns through lawful processes. They buy guns directly from gun shops, or they buy them at gun shows, or they buy them from private sellers, all of which are legal methods of buying guns. There is of course a black market for guns, but if you're too stupid to acquire a gun legally, you're probably going to fall for the obvious FBI sting operation that calls itself Black Market Firearms dot com. I'm not linking it here, in the off chance that it really is an online retailler of explicitly illegal firearms and ammunition.

The point is, most gun control legislation is aimed at the methods criminals use to obtain guns. Restrictions on straw purchases, requirements for background checks at gun shows and for private sales, requirements to report lost or stolen guns, these are all reasonable restrictions that don't take guns away from lawful owners.

It's crazy how the criminals in Europe tend not to use guns anywhere near as much as the U.S.