I love it...if only it was that simple.
I have one because I like to do several different types of target shooting, and the AR-15 is versatile enough to do them all pretty well. My Colt/Spikes is a bit heavy for CQB, or Three Gun, but it works regardless. It's capable shooting MOA consistently with the right ammo so I can shoot groups off the bench, or out to 600 m at Petawawa off the Bi-pod. It's three rifles in one!!!! If you're not swimming in cash it's a great buy on versatility alone. Speaking of cash, it's also cheap to shoot.
I think Rod is mistaken bringing up the idea that it protects more lives than it takes. I downplay that whole side of things. I point out that IN CANADA, I can't recall a single incident involving an AR-15, it may have happened, but I no memory of such an incident, nor could I find one using Google (my Google Fu isn't well developed though). I also love refuting the whole high power death machine thing. It's a center fire rifle after all so it has some "balls", but in the grand scheme of things it's a pipsqueak.
Unfortunately people as a group are pretty dim, and pigheaded. If the facts don't fit their narrative they dismiss them outright. I've had this discussion with friends in the past, at times I feel like I'm talking to a floor tile instead of an "intelligent" person.