When people who are not familiar with firearms see a picture of an AR-15, they have the tendency to overreact for a number of reasons.
The AR-15 has a serious PR issue. It's feared and held up as the shining example of civilian gun ownership gone too far. Many call it a "military-style assault rifle" or the "general rifle for the U.S. Army."
The AR-15, originally designed by Armalite but now manufactured by dozens of companies, was the basic platform upon which the M16 was built for use by the U.S. Army. Its design was sold to Colt, who made a very different firearm and sold it to the military.
The AR-15 is a civilian version of a military rifle. It's not an assault rifle, since an assault rifle has the ability to go fully automatic. In fact, the term "assault rifle" itself comes from the German Sturmgewehr, a term they used in 1944 to designate the first fully-automatic rifle. So calling it an assault rifle is a bit of a misnomer.
Is it a black rifle? Based on color, yes. Is it a tactical rifle? Well, you could make any rifle a tactical rifle, if you used it in a tactical way. Call the AR-15 what it is: a semi-automatic civilian rifle, not any more dangerous than any similar firearm in the hands of an experienced shooter with ill intent.
One of the most common fears surrounding the AR-15 is that it's a weapon used for mass killing and that its ability to accept high-capacity magazines facilitates this purpose. An excellent YouTube video showcases why this ability is not much of a game-changer, yet high-capacity magazines are routinely blamed as one of the perpetrators of gun violence.
I'm a relatively experienced shooter, and I can change an AR-15 magazine in a little less than 6 seconds. If you were to train to do so, you could cut that time down considerably. The magazine capacity of an AR-15 (by the way, they make 100-round drum magazines, if you're really determined to be worried) shouldn't be one of its distinguishing features.
A key feature of the AR-15 is customization. It usually comes with adjustable stocks, pistol grips, and the often-misunderstood barrel shroud. Again, we see a vilification of the rifle based on its ability to accept a bevy of accessories, including grenade launchers, suppressors, and bayonets, which are respectively illegal, illegal, and incredibly impractical. In a similar vein, the fact that you can adjust a stock, mount a sight, or grip a barrel shroud doesn't make a weapon more or less deadly. You can do all three on almost any rifle and most shotguns. The AR-15 is not more or less deadly because you can attach things (including a beer-bottle opener) to it.
There are real discussions to be had about gun violence in America. Even the strongest Second Amendment believers will acknowledge that firearms play a part in American culture that can have devastating national effects. But there isn't a way for both parties to come to the table to have the discussions if one side can't objectively look at the issue.
In order for "smart" gun legislation to be passed (even though in my opinion, no legislation is the smart legislation) the population needs to understand the firearms they're attacking, vilifying, or banning. Less than .05% of gun murders are committed by rifles. It is unknown how many incidents in that minuscule statistic can be attributed to AR-15s, but until we move past the idea of the AR-15 being a "tactical tool of murder," we will never be able to have an intelligent discussion about gun violence.
The photo is the author's AR-15.