A few decades ago, various European countries changed the type of natural gas used for home heating and cooking -- replacing a toxic form with a harmless variety. That step eliminated one time-tested way of killing oneself. Alas, while the number of gas suicides declined, in most of these countries, the death toll didn't.
The same pattern holds for guns. The National Academy of Sciences report noted that any link between firearms and suicides "is not found in comparisons across countries." The number of guns in a nation tells you nothing about its suicide rate.
But let's suppose science could establish that people who obtain firearms do indeed increase their death rate (or the death rate of their family members) from suicide. So what?
Buying a car may shorten your lifespan, since traffic accidents are a major killer. Building a backyard swimming pool creates a potential fatal hazard to you and your loved ones. But nobody says the government should interfere with such decisions.
Personal safety is a far more central matter of individual autonomy than those choices. A mentally stable person living in a crime-ridden neighborhood should be free to judge whether she's more at risk from street criminals than from a spell of intense depression.
Presumptuous paternalists argue that Americans should be deprived of guns because gun owners are their own worst enemies. A lot of Americans would reply: We can't trust ourselves, but we can trust you?