You dont need a reason to have an AR15...its a damn AR15!
I have 3 of them.
1. Fun to shoot
2. Cheap to shoot
3. Lightweight, deadly accurate, and highly effective at any reasonable range.
4. As good as it gets for L.E./ self defense/SHTF.
5. Tremendous psychological impact due to the "military look."
Resistance is futile. You will be assimilated
Because I was going broke shooting my first black rifle which was an M1A (still an awsome rifle). .223/5.56 is half the price of .308, so I figured why not. First time I pulled the trigger on my Colt M4 I was at a crowded range and I honestly wasn't sure if it even went off. Thought maybe I'd loaded it wrong, or forgot to turn off the safety, or it just malfunctioned?.. I was so used to .308 recoil my shoulder felt nothing. That's when I realized why they're so popular. But I'm still not playing favorites. I love both my evil black rifles equally.