Bump firing is dangerous for a couple of reasons. Primarily, it is dangerous because it is typically the result of a poorly controlled weapon. Second, poor handling of a weapon can cause it to malfunction.
Traditionally, there is a basic principle of physics that defines the mechanics of a semi-automatic weapon. For every action, there is an equal and opposite reaction. This is why recoil exists. When you fire a semi-automatic rifle, the expanding gases from the round cause the bullet to be forced out of the barrel, and usually, a tube connected to part of the barrel will cycle part of those gases back into the weapon to cycle the bolt, chambering a new round. The rest of the forces from firing are channeled backwards, into the shooter. But the handle of a handgun or stock of a rifle causes this force to be distributed evenly, rather than into a single dense projectile.
Small arms design assumes that someone is going to be holding the gun properly. If the force of firing a round is improperly distributed, the slide may not fully cycle, or the bolt on a rifle may not fully cycle. Sometimes, this just results in a jam. But sometimes, it causes slam-firing.
Slam-firing is when one of the components that fires a weapon does not fully cycle, causing it to fire the weapon again *without* the trigger being pulled. A common example of this is in old models of the Russian SKS, where the firing pin sometimes did not lock properly during the bolt's cycle, meaning it immediately struck the primer of the next round as it was being chambered.
I shouldn't have to tell anyone, gun savvy or not, how bad it is for a gun to fire a round without that round being seated properly in the gun. It can cause an explosion in the barrel that destroys the weapon and the shooter's hand. It can cause the other rounds in the magazine to "cook off", firing them all at once and destroying the shooter's hand. Most of the other possibilities here also result in someone's piano-playing days coming to a premature end.
I don't really have a conclusion for this article, so I'll just dispense some firearms advice. The primary problem with guns in this country has nothing to do with legislation. It has to do with poor discipline and a culture of disrespect.
The modern firearm is a fascinating, technically ingenious work of art, the result of over a hundred years of incredibly clever people being incredibly clever. When you mishandle or misuse a firearm, you are disrespecting those inventors, you are disrespecting how clever they were. You are disrespecting a work of art.