Many people who are “gun guys” (or “gun gals”) do not understand why anyone would need, or even want, an AR-15. Here’s a useful article partially addressing the topic. Highlights:
People like the AR-15 because it is relatively lightweight, relatively small, easy to accessorize with things like lights and scopes, the controls are intuitive, and it has a cool factor from video games, movies, and military heritage. It is easy to shoot it relatively accurately. It is easy to hold and carry compared to other rifles. Its size and weight make it particularly attractive for people of smaller stature.
…I think you would have a tough time proving why you need to ban the AR-15, and I think you would have a tough time even defining an AR-15 well enough to ban it, and I think you would have a tough time proving a ban once-enacted has done any good at all. Prove me wrong — I’m willing to listen.