While discussing the potential for a gun ban in the United States I realized that the pro-gun-ban people genuinely believe that banning guns will save lives. In an attempt to facilitate debate I discovered that getting down to the numbers helps discover where their math is different from the pro-gun position, it is these points we can focus on to help them see the light. I put this sequence of equations on a spreadsheet but you can talk someone through them without one. For each value get the person you are speaking to, to give you their value. I've using example numbers with a typical anti-gun leaning.
A: Population: That's an easy one, about 311,000,000.
B: Number of people killed with guns in America each year, I don't have exact figures for this but it's about 6,500. [JWR Adds: According to Bureau of Justice Statistics, the actual figure was around 11,100 in 2011, and has been in decline since 1993.]
C: The percentage of people who would be saved if guns were banned, lets say 50%. (Clearly it's not 100%, since illegal guns would still be used, while pro-gun people may claim that the number would actually increase, lets not waste our time on this point just now.)
D: The number of additional people who would be killed because criminals would become bolder with less to fear from disarmed victims and would-be-victims who today can defend themselves who would be helpless once disarmed, lets say 200.
So, the total killed with easy access to guns = B (6,500) Total killed without easy access to guns = B*C+D (3,450). Pro-gun people typically get bogged down at this point debating these figures, but they are only one piece of the story and it's a small piece. Agree to disagree and move on, say something like "While I disagree with those figures let's accept them for now and move on." What about government-driven Genocide events against their own people? These occur very infrequently, but when they do the loss of life is often in the millions. The problem is they are very hard to calculate and most anti-gun people put the chances at zero. This is where the pro-gun argument clearly defeats the anti-gun argument it's here we want to spend our time opening the mind of the the anti-gun people. Estimating the probability of a genocidal event initiated by the US government and the resultant loss of life is very hard so let's look at the world average for the 20th Century:
E: Average population of the world during the 20th Century. Obviously this varied but let's say that the populated started about 5,000 Million and ended about 7,000 Million. So the average is about 6,000 Million.
F: Number of people killed by their own governments in genocidal actions during the 20th Century: 170 Million. (You can find evidence to back this number up pretty easily just by a quick web search)
G: Number of people killed by their own governments as a yearly average during the 20th Century = F/100 = 1.7 Million
H: Probability of a person being killed per year by their own governments as a yearly average during the 20th Century = G/E = 1.7M/6000M = 0.000283
I: Average number of Americans killed per year by their own government in genocidal actions = H * A = 88,116 That is roughly 88,000 Americans would die on average each year if the American government were capable of and intent upon taking some form of genocidal action against the American people. Of course it wouldn't be 88,000 each and every year, it's more likely to be 200 times this number once every 200 years or something similar but we're dealing with averages here. Now the anti-gun people will typically walk right into you logical arms by pointing out that America is not a 'typical world country', it's existed longer than 200 years without a Genocidal event. (Let's not get into discussing some of the things Americans did to the aboriginal ("First Nation") people some of which look very like genocide). "A genocidal event is less likely to happen in America", they will cry. Is it? Why is that? Oh yes, it's because the 2nd Amendment allows the population to be armed to discourage any such attempt!
J: The probability that a Genocidal event would be attempted given an armed population: Let's say 25%? It could happen but it's a lot less likely.
K: The percentage loss of life if a Genocidal event were to be tried against an armed population versus an unarmed population, certainly people would still die but it's probably going to be fewer people because the people will be able to defend themselves. Even if it's only by being able to lay down covering fire while they flee. Let's be 'generous' to the anti-gun people and say no fewer than 80%.
So looking at Genocidal events we have Without guns: = I = 88,116 people / year With guns = I * J * K = 88,116 * 0.25 * 0.8 = 17,623 people / year
Totals so far: Losses of life with an Armed population per year: 6,500 + 17,623 = 24,234 Losses of life with an unarmed population per year: 3.450 + 88,116 = 91,566. We can stop here and try and let those numbers sink in. An Anti-gun America doesn't save 3,050 lives a year (6,500 - 3,450). Long term, on average, it would cost 67,443 lives a year (91,566 - 24,123).
Or if you want to hammer things home you can do similar estimations based on loss of life from any external country attempting to invade America. Once again an America with an armed civilian population is less likely to be attacked and the losses will be smaller as the population can defend (or worst case lay down cover for a retreat) versus an unarmed population who are ripe for slaughter.
Also you can point out that the 1.7 Million people killed by genocidal events per year by their governments in the 20th Century is an average across the whole world. If you look at the events behind these figures in detail you see that by far the majority of these were killed after government disarmed the people. Thus logically these killings are less likely to happen to an armed population and more likely to happen to an unarmed population.
We reduced the value above (factor J) for an armed population but we didn't increase it for an unarmed one (I). Without knowing what percentage of the world population were armed versus disarmed across the 20th Century we can't really include this in our calculations but we can be confident that the average of 88,116 deaths per year for a population the size of America is a very conservative figure, it's probably well over 100,000.