I mean does anyone actually need to go anywhere by car at speeds which are capable of of lethality? :s like your point there is only so far we should regulate things due to a tiny fraction of a percent of mad people.
I think making comparisons like that to guns is just not really feasible because guns are different. Saying nobody should be allowed scissors, a car, rope, knives, baseball bats etc..... yes they can all be used to kill, but they have multiple uses. You don't use a gun to do anything other than inflict damage to a person/animal, or in high calibre military guns, actual vehicles/buildings. They are purpose made weapons. The actual legitimate required use of said weapons (other than shooting them for "fun") is so, so, so minute, that in the interest of preventing even a small amount more of potential scenarios as per the op, the laws could even be made stricter to take them out of play for anyone other than those that truly need it, such as possibly farmers for pest control.
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I don't agree in a family homicide case. Think about how traumatic it would be to kill a family member you love/loved with a shotgun at very close range. You'd have to be very disturbed to do it. If you get it wrong you could blow their arm or leg off and then you'd have to shoot them again to kill them fast. The amount of blood, gore and brain matter etc from a head shot would be absolutely horrendous, you'd be emotionally scarred for life by it. Just hitting them hard on the head with a club hammer when their back is turned to you or stabbing them in the heart with a kitchen knife when they are not expecting it would be far less traumatic for you. If they suspect nothing then you could kill them while they are asleep so that they don't suffer and there isn't a bloodbath. Shotguns at close range make a terrible mess.
You are saying that it is easier and less traumatic to stab/club someone to death as opposed to pulling a trigger on a gun? If you want to kill someone, even if you muck up the first shot, you can probably find the will to pull the trigger again quite easily.
There is loads more that can go wrong with a knife/hammer in that the victim may flap arms around and struggle, causing injury to the attacker. Also stabbing is unlikely to kill very quickly unless you are very specific. The wound may be superficial and cause extreme pain and then screaming. They may run off. Loads of stuff could go wrong.
Compare that to pulling a trigger... I mean there's no contest. Guns - by their nature - are easy killing machines.
Your argument is that a shotgun would do so much damage that the attacker would be traumatised and stop. I think if you have got to that point where you pulled the trigger, suddenly seeing someone decapitated is not going to make you suddenly be like "oh wow it does that much damage...I should stop".