Both cases are very unlike the US. Japan was basically disarmed by the US after World War II, much like Germany, and Switzerland is a neutral "bank of the West" country with a militia instead of a professional army. We could take Britain and Canada as two cases that are more like the US. Canada has liberal gun ownership although unlike the US its role in international conflicts is smaller or secondary. Britain, on the other hand, has a more active role in international conflicts, approximating the US in that sense, but restrictive gun laws. The US practices colonial or invasive military activities, which requires glorifying the military and indoctrinating the population on how correct it is for it to be strutting around the world, and has liberal gun laws on top of that. Add to this highly competitive "you're on your own" jungle capitalism policies and ideals, and what else can you get than occasional freak attacks like this one, with all the guns lying around? If the nation teaches its people that kicking ass is the way you get anywhere, they will do it too on their level and in their way.
I envy Switzerland and Japan.
You always have some people that stretch arguments in any camp, so that's not really evidence. You're just depicting people with more restrictive gun policy ideas as people who want to ban all guns.
and it shows in that a lot of the people who'll say "gun control isn't the same as disarming" will also go on to make another argument about how guns won't help you in a dangerous situation anyway, there has been plenty of situations where lives have been lost as a direct result of gun regulation as well.
There are situations where people with guns can stop violence, but even those need regulation. A gun at home may be more or less understandable, or even at a store, although the more public the situation, the more a warning may be necessary, such as an "armed guards present" sign. Uncertainty is a big factor in violence and violent death. An undercover cop, an armed officer that's not in service or an armed civilian can be in danger or increase danger if armed criminals show up because of how they may react if he tries to draw the weapon, and from what they may do to him if he doesn't and they spot his weapon. That situation may force violence that wouldn't happen if victims weren't armed or if the cop were easily identifiable. In the latter case because it's likely the criminals will go look for an easier opportunity, instead of facing a cop. Private and undeclared armed defense can stop crime, like theft or even some aggressions, but it's not as good at saving lives, even while it can still do so sometimes. The real question behind all this is how much private property is worth compared to lives and peace.