I have an AR-15 and I have not hunted with it except to kill coyotes out on my farm that have been killing calves and chickens. What I enjoy about the rifle is going to the rifle range and hitting my target at 100, 200, 300, 400, 500, 600 yards. Now I grant that I had this rifle built to very small tolerances, specifically for the accuracy. It is the joy of shooting that I bought that particular rifle. I have spoken to my gunsmith about building a 338 mag for long range shooting and hunting. I have seen his rifle hit a 2 inch target at 1200 yards. When he told me his rifle would do that consistently, I did not believe. I saw the rifle being used and it was true. These are amazing firearms, and very fun to shoot. This is one pursuit of happiness.
That is all you need to justify owning it.
There is no "sporting purpose" or requirement to demonstrate "need" as the gun grabbers imply.