It's a lot easier to take some guns off the market than to change human nature.
Therin lies the problem. It sounds as though this person is less interested in actually solving the problem than he is in quick, easy, feel-good action. The problem herin lies that there is no quick, easy, feel-good solution to the problem.
Try putting it to him this way, banning guns in an attempt to stop violent crime is akin to banning computers in an attempt to stop the distribution of child pornography. Sure, it would be more difficult to distribute such filth without a computer, but it certainly wouldn't stop it. The fact of the matter is that people have, throughout history, come up with newer and more creative ways to do evil upon one another and removing one tool will simply make them turn to another.
A firearm isn't the only, or even most efficient, means of killing a large number of people. A crude pipe bomb wrapped in duct tape and nails could be used to unleash just as much, if not more, horror than any gun. Worse yet, while there are certain safeguards in place to try to prevent a criminal or mentally unstable person from getting a gun, anyone with an internet connection can figure out how to make a pipe bomb quite easily.
The cold, hard fact is that there is no quick, easy panacea to cure the problem of violence. Even if we could wave a magic wand and make all firearms disappear tomorrow, people would still find ways to kill each other. By and large, evil people are a cowardly lot who prefer to inflict their malice on those who are smaller, weaker, or at some other disadvantage to them. A firearm serves as an equalizer of sorts in that it removes, or at least goes a long way towards removing, the advantage of an evil person. If someone who is larger, stronger, or part of a group of like-minded people is able and willing to harm you, a firearm is your best chance for survival. The Second Amendment isn't about hunting, target shooting, or other "sports" but rather about the fundamental right to defend one's life.