It's not, but ignorance is calling the shots (no pun intended) in our country today.
Here are a few facts:
Assault weapons have the ability for full auto or burst fire. While they're legal to own, they are VERY heavily regulated and extremely expensive. It takes at least a year to get one. Thereafter, the ATF can inspect the owner's full collection on demand, making them weapons that most gun collectors have no interest in owning.
To the best of my knowledge, NONE Of the mass shootings in our country have involved fully automatic weapons - except in the hands of officials responding to the incident. Someone correct me if I'm wrong.
"Assault Rifle," conversely, is a recently fabricated term that has no real definition. It pretty much means "any gun that the Left doesn't like." That's how desperate and nonsensical the Left has become.
Most on the Left think that the "AR" in "AR-15" stands for "Assault Rifle." They're wrong. It stands for "Armalite Rifle," ArmaLite being the company that invented the AR-15 back in the '50s.
An AR-15 is NOT an "evil black gun." Its components are modularized for easy replacement, so it can assume almost any look. Everything from stock to barrel can be replaced to give the owner the look, features and functionality he wishes, EXCEPT for automatic firing. That can't be done, except illegally. AR-15s come in big sizes and small sizes. They can be made to accommodate almost any round.
The AR-15 is a popular but ordinary semi-automatic gun that can be made to look "cool." It's nothing more than that. The Left... operating out of ignorance... finds it particularly frightening.