1 While this may seem callous, I don't really consider accidental/negligent shootings all that important in the broad scheme of things. Yes, it's horrible they occur, but, to me at least, they are roughly the same as any other kind of fatal accident. Children shouldn't necessarily have unsupervised access to firearms, but the same can be said about the chemicals under the sink, or the backyard swimming pool. There can be, and are, failures in safety in all walks of life. Seat belts definitely reduce the risk of injury/death, but people wearing them still die in car accidents all the time. There are no guarantees in life, except that it will be over one day. The actions of criminals and the mentally disturbed cannot be prevented nor predicted. To lay the blame for their actions on others is ludicrous at best. Call it a silly argument, if you will, but "taking guns away" in some form or another will not stop violent acts of depravity. Look up "Timothy McVeigh" some time.
2 Not much. Maybe take them shooting at a range some time, if they are at least a little reasonable, so they can see that the mere presence of a loaded firearm doesn't equate to death and dismemberment. Frothing-at-the-mouth types will never change though.
3 Depends. There are hunter safety classes, general usage classes, required classes for certain things, none for others. I've heard the back-and-forth over this topic a few times, and it's hard to really come to a definitive conclusion. The Four Rules aren't that hard to figure out. Should a person be required to take a class for each gun he/she purchases? Or by gun type, ie pistol vs rifle vs shotgun, etc? Or should it be a monthly/quarterly/yearly thing? Doesn't going to the range count as training? What if I purchase certain guns, like curios and relics, with no real intention of ever taking them to a range? I have an old Mauser in an obsolete caliber that would be more of a hassle to buy ammo for than just letting it look cool in the safe. Should I be required to take a safety course for something that is essentially a decoration? I'm certainly not against training, but I don't know how a training requirement could be implemented satisfactorily.
4 Zen. Going to the range is a great way for many people to let go of everything and focus on what's in front of them right then and there. As a simple hobby, I, for one, have always been fascinated with the intricacies of the mechanical nature and histories of firearms. Going to the range, maintaining or building, talking about them, etc, are also good ways to pass the time with family and friends. Chalk that up for bonding experiences and socialization. I do have an issue with this question as stated, however. Dude, you're Swiss... How can you say "stay realistic" after mentioning defense against invasion? Also, consider that some people in the USA live pretty close to what could be described as a war zone. Those Mexican cartels are no joke. There have been a number of incidents where US citizens have been attacked, kidnapped, and/or killed by groups of foreign nationals over the past few years. If you've read enough posts, I'm sure you've heard the "but your puny gun is no match for a tank!" line that gets trotted out from time to time. It may be true that common gun-owners are outgunned by the likes of the military, and police in some areas, but that isn't an argument for more restrictions so much as a revelatory glimpse at the discrepancy between what "they" have and what the citizens are being denied.