The first thing we need to do when discussing gun control is to clearly outline the pros and cons of the situation. In other words, we need to first list the reasons why gun control is 'needed' and the problems for which gun control will be a solution. Next, we need to list the effects that gun control will likely have and the civil liberties infringed upon by any such law. And then finally, we need to figure out how to craft legislation that fulfills the first set of objectives while doing as little harm as possible with the second. In this case, if we are talking about the repeal of the 2nd amendment, we need to characterize the legislation as "granting government total and unfettered ability to ban gun use among anyone for any reason at any time"
Pro:
"Gun control will save lives." This is the primary reason, in fact usually the ONLY reason, why people advocate infringing on the right to bear arms. However, when we look at this element, we see that it needs further clarification. How exactly will it save lives? Whose lives? How many lives?
There are several different types of people killed by guns. Roughly speaking, they fall into 4 different broad categories. Robbery/premeditated murder victims, victims of rage violence, victims of mass shootings, and accidents. By 'rage violence' i mean everyone killed by someone in a fit of rage but not a premeditated crime, i.e. road rage, or getting killed in a bar, or a man shooting his cheating wife. As noted by others in this thread, these categories are affecting differently by gun control.
Gun control will have zero effect on robbery/premeditated murder or on mass shootings. If someone is planning to commit a crime already, the added penalty of using an illegal weapon to do it isn't going to deter them at all. At best, they'll simply switch to a different weapon like explosives or poison to achieve their objective. Oklahoma City killed way more people than that idiot in Tucson ever could and no guns were used there.
Gun control's effect on rage violence as well is fairly minimal. Contrary to what some people think, guns aren't the only way to kill someone. Before firearms were invented, people committed the same stupid crimes and did it just fine with their bare hands. Really, the only effect would be that the victim would almost always be a physically weak person, usually a woman, and a large, strong attacker would have less difficulty subduing an unarmed victim. So we'd just convert a lot of rage shootings into rage beatings-to-death or rage stabbings. Not precisely a laudable goal.
Where gun control WOULD have a significant effect is in the area of accidents. However, the question later on is whether preventing accidental shootings is worth the cost. And no, "every life is precious" isn't valid. Encroachment upon fundamental civil liberties is often more important than a single life, or even a few lives. "Give me liberty or give me death" as it were.
Cons:
And here is where we look at the detrimental effect of gun control. This comes in two basic flavors. Immediate effects and long term effects. The immediate effects are things like lack of self-defense or a rise in black market trading of weapons. The simple truth is that we don't really have accurate statistics on just what the immediate effects will be. However, we DO have a study that indicate that guns were used defensively 2.5million times annually, and a study that shows that gun-owners are less likely to be injured in a robbery or assault than non-gun-owning victims. So, given these statistics, and basic common sense, one would have to admit that the immediate effect would include a rise in people being unable to defend themselves from criminals. The second immediate effect would most likely be a rise in crime, specifically the illegal sale of firearms. History has shown that whenever a prohibition on something goes into effect, the first result is almost never the total elimination of that thing, but usually a rise in flouting the law. We've seen this with drugs and alcohol, and even more directly with weapons in the American Revolution and the Jacobin Rebellion (even when the brits completely banned all weapons from the scots, they still managed to hide anything and everything they could). At best, law enforcement will just ignore the law, at worst we'll see a thriving smuggling trade.
And then we have the "long term" effects. The truth is that the constitution, despite its age, was a rather forward thinking document. Many of its protections and privileges are not designed for the best case, or for the normal case, but for the worst case. When most people think of gun control, they are thinking of right now and of reasonable restrictions. But that's not what the 2nd amendment was written for. The 2nd amendment was written for when the American Nazi party comes into power and starts rounding up people. It was written to prevent laws like "All blacks and hispanics can't own guns". It was written to safeguard the ability of the individual to protect himself and his freedoms when the government is unable or unwilling to do it for him. Being able to defend yourself is as fundamental a right as being able to speak freely. In fact, the ability to speak freely does not exist without the right to defend yourself. Sure, while the courts are free and working, you can rely on them to protect you. But what happens when they aren't? Too late then no?