For varying degrees of "works":
1. Gun supporters argue that gun control laws are mistakenly focusing on the tool, not the motive (where motives are tied to actual causes). It's all a moot point if someone isn't trying to commit murder. If someone *is* intent on committing murder, then if they succeed with a knife instead, then gun control had no effect on saving innocent lives. Innocent lives were still taken due to the fact that the issue is the motive, not the tool. All you've succeeding in doing is disarm a law-abiding *citizenry* while retaining a heavily armed government (which isn't affected by such laws).
2. Reduction in the use of guns and subsequent increase in the use of knives doesn't mean that criminals can't get guns or that *no* guns are used overall, it merely means that there are cases where they saw no need for it in order to commit the murder. If the situation really warranted a gun, then they'd still just get a gun through illegal channels.
3. It's always shaky ground to compare gun crimes between countries, because again the point of gun supporters is to focus on the cause of the motives for crime instead of focusing on the tool. For example, European countries bordered with other European countries is a different problem than being bordered to Mexico (which in turn is chained to South American black markets). Much of gang violence and inner city violence and poverty is tied to the socioeconomic effects of the illegal drug trade. If a European country doesn't treat drug use as a crime (rather than a public health issue), or if recreational drugs are legal, then they have no 21st-century-Prohibition black market like the U.S. The U.S. teaches about Prohibition of the early 20th century, but not the lessons. Cultural goals also differ. You have to ask just how much you're willing to give up in order to have a perfectly safe world.
4. Statistics and damn lies, etc. One set shows guns up, crime up. Another says guns down, crime down. But yet others say guns up, crime *down*. Still others say guns down, crime *up*. So the question is this: does that mean the debate is at an impasse? The answer is NO. Guns are logically demonstrated as *not* the primary cause. How does this logic work? Like this: If the claim being refuted is "more guns equals more murder, less guns equals less murder", then it is *not* required to show that guns improve the situation *everywhere* you go. It is only required to show *one* instance that exists that refutes the claim. Those situations exist, therefore that means that the primary cause or causes are *not* guns. Other causes are the real causes. Perhaps guns are enablers as secondary causes, but in practice nothing anyone cares about will be solved by band-aids: the primary causes must be addressed first.