Let's take heart disease, for example. Can someone walk up to a healthy person and instantaneously give them heart disease?
Method and execution counts. A gun is a man-portable device that allows someone to project lethal force at a distance. Looking at other causes of death that use similar methods is reasonable and good.
Until someone can teleport arterial plaque into your veins at a distance without your consent, I don't find the "all other causes of death" argument to be persuasive.