Gun control is the political idea of imposing strict controls on the possession and use of firearms and it is opposed by the gun rights movement. Gun control is commonly supported by the liberals, while the opposite view is held by most conservatives.
The possession of firearms is often argued as the person's right, and in USA, this has been enshrined in the Constitution as the Second Amendment. However, the said amendment was written at the time when firearms were incapable of automatic fire and were far less accurate and lethal than now. It didn't account for either the submachine-guns and assault rifles, which were always designed for military with the express intent of killing as many people as possible, nor the modern lightweight and easily concealable pistols.
The results of these modern advancements can be easily felt in countries with lax gun laws like America. The gun-related deaths are amongst the highest in the world, with many spree killings like the school shootings.
The easy availability of weapons also leads to higher rates of suicide, as it is much easier and quicker to do so with a specialised tool then a makeshift method like hanging or overdose. Even if you're a supporter of euthanasia and believe that it's best to die quickly by own hand without suffering, suicide WASN'T something planned for a long time for most people who ended their lives this way, but a spur-of-the-moment thing. For instance, coal gas-fired ovens (which produced large amounts of poisonous carbon monoxide, so that putting a head in the oven was an easy way of killing oneself) amounted to almost 50% of all suicides in Britain in 1950's. When they were outphased, the suicide rate fell by a third and it never recovered. Similarly, when the Ellington bridge in Washigton (which used to amount for half of the city's jumping suicides) had a barrier installed to prevent jumping off, the jumping suicide rate fell by exactly the same amount, even though there was a Taft bridge near it, which had the same 125 feet drop and lacked such barrier and yet hadn't experienced a rise in jumpings one would expect. As such, reducing the opportunities to do by decreasing the number of guns is one of the more efficient ways to reduce the number of suicides. 1
One of the common arguments against gun control is the idea that it will create black market like with drugs and give advantage to criminals as no-one outside police will be able to resist them. This is a flawed argument, as it ignores the fact that guns are a lot harder to smuggle in then drugs, as thy're both much larger and thus harder to conceal, and cannot pass through the metal detectors. Unlike drugs, guns are also much harder to manufacture illegally; crafting guns personally requires extensive metalworking skills, which the average criminal isn't going to have, while the 3D printers cannot make the high-pressure parts of a gun. The second part of the argument is also easily addressed by the existence of non-lethal self-defence weapons like gas sprayers and stun guns, which adequately protect the user while having much lesser potential for misuse. 2