So the movement to remove the AR15 continues to grow (and personally the idea of gimmick items like the 'bump stock' are nothing more than a joke and would NEVER degrade any of my rifles, no matter how 'cool' it might be to blow off wads of cash like a drunken college kid at his first strip club!), the question is WHY it is so popular?
In my humble opinion, here might be a few reasons:
For NOT being a military rifle, they have the same look and feel, and I will say that most gun guys I know like that at some degree. Also, for those who did serve in the military, this is something they are very familiar with (as my father once put it: "It's like my 16... and I slept with my 16").
When done legally, you can even have a Short Barreled Rifle configuratuion with a suppressor that measures the same as a standard rifle (Yes... and when I say 'legally' I am talking about filing ALL the necessary paperwork with the ATF, pay each of the $200.00 tax stamps (in this case there would be 2), and then waiting up to 11 months (shortest time I have ever waited was 7 months for a suppressor, but my SBR'd receiver was 8 weeks)before you can actually put it together without risking 10 years in Federal (bang you in the a$$) prison, and I believe it is now a $250,000.00 fine!
The AR15 is a cost effective rifle. The 5.56/.223 round is plentiful and inexpensive. FMJ (Full Metal Jacket) ammo can be had for about $40 for 100 rounds. This means that it won't break the bank to go out and put some rounds through it. I would wager the only other rounds cheaper than this are going to be .22lr and 9mm, both of which are very good for their purposes. This removes the excuses of not being good with it, familiar with it, etc... because at those prices you don't have an excuse not to practice!
You can make them look cool! Go out on some of the pages, and there are guys really making some almost showpiece grade rifles. Way too pretty to be used in the mud and dirt on a battlefield. The people who make and work on rifles like these have no desire to go and shoot up an office building, school, etc... these are more like a functioning piece of artwork. Something you can make and still use.
Following up on this part also, is the fact that the receiver can be easily modified if you want to change things like the stocks, barrels, and other accessories out. This does a couple of things: It allows you to have a single registered receiver (the part that classifies as the gun itself) that you can make functional for different things. I might have a 20" barrel that I use for hunting coyote that harass my sisters horses, or a 16" carbine for basic usage, or a 10.5" SBR that I would mount a suppressor onto for home/property defense where I might not have time to put on muffs/ear plugs to drop down the 165+db sound of each shot (where with a good silencer/suppressor/can it can be brought below 140db which is classified as Hearing Safe), prior to it going off in a potentially tight area like a hallway or screened in porch. This last one is something that nobody really wants to talk about: hearing damage. God forbid I would ever have to use one of my guns for defense in the home, the sound a shotgun or pistol produces is horrendous, and a rifle is worse! Now in the heat of the moment, I am not going to care, but the damage to my ears would be permanent for sure and I for one would never want that. I want to be able to grow old and listen to my future family without the use of hearing aids if at all possible, and most of all... like most gun owning Americans I want to do this with NEVER having had to use any of my weapons against another person.