I do know how it feel killing by firearms and by knife, I am probably one of the few people here that actually did kill a person with both firearms and bayonet in war. I know how it feels.
What you are describing is what happened immediately before you pull the trigger and immediately you stick a knife in someone. The "threshold" is not as big as the one that, when you make a decision somebody is going to die today.
Problem with people view with firearms (I will refer to gun from now on) is that it's not upclose and personal, where you detached from the reality of someone is going to die and killed by you. The problem is, this is already accounted when you decided to kill in the first place, once a person have decided he or she will kill someone, the choice of knifes and guns are only the weapon of choice.
Think of it this way, if you are of sound mental health, will you increase your urge to kill when I handed you a loaded gun? If I hand a knife and a gun to a normal person, they won't say "ah, I got a gun now, I gotta shoot someone" People who, on the other hand already have made up their mind to kill, already had the wheel in motion, and choosing a gun or a knife to do his/her deed is just a process. Because you already have the mind to kill. And that's abnormal to begin with.
I will concede that killing people with a gun is way more easy than knife, but at the end of the day, it is the nature of mass killing, a one off, planned attack over a large area, people who prefer to kill with a knife usually more calculated and more plan have to put in motion, that did not fit the profile of a mass murder, it more suited with the profile of a serial killer.
On the other hand, gun control would have no use in these situation, in fact, gun control would only make the course of killing easier, because you are less likely to encounter armed resistance during your deed. People who usually do this kind of stuff would have had his weapon illegally, or obtained with the fact that they are legally covered (like belong to a gun club or some sort) Both of which would have by-passed gun control law. Even in Australia, gun crime is actually a problem when Australia have a strong gun control culture, to an effect that you cannot own toy gun (A friend of mind actually was charged by the police for selling toy gun, those shooting water bullet from China, and he got charge like he is a big arms dealer....)
The overall problem I see is the mental health problem and lack of mental health care, as I said, if you are right in your mind, you wont go down and kill a bunch of people when I handed you a loaded gun, people have to be sick in the head before something like this is done. And we aren't doing enough to care for these people, which is how this turn out.
