"Assault Weapons" and Utah stabbing

How can people be so ignorant. The logic they apply to situations completely escape them when questions related to firearms are applied by the same principles.

"After the knife was purchased, He turned it into an assultweapon and started stabbing people" - which was quoted from a bystander at the sene of the crime in Utah.

Applying the same logic and reasoning, how is a rifle or firearm automatically labled as an assaultrifle, assaultfirearm, or assaultweapon? As with knives, bats, blunt objects, it isn't an assault weapon until some criminal puts it to that use. By this, and the only logic reasoning one can truly use and justify, assault weapons don't exist. If one can't understand that irrifutable logic and truth, they shouldnt be allowed to have any creditable influence in this matter.

Honestly, are lawmakers that ignorant and/or shady, or are we that stuipd to allow officials to attach assault to anything they choose?