The bullets are too small (.223/5.56), I prefer a AR-10, it shoots a .308/7.62x51.
1. The 5.56 was developed for military use, when you have all of your armed buddies with you. Some of those buddies may be small and/or are women. In general, smaller people don't like shooting a full-power rifle. I am not small.
2. In a military battle, getting shot with a .22 will take you out of the fight. Killing the enemy isn't necessary. It may be when it's just you vs. some thugs.
3. More power is better. The .50bmg or a 338 lapua will deliver more power. Sadly, the 338 lapua and .50bmg costs 5 bucks a round. A .308 cost about 0.30, which by comparison to .50bmg is not much more than 5.56 at 0.20.
4. Unlike the military, I will not be supported with grenade launchers, machine guns, planes, tanks and ships. I may need a gun that can shoot through light vehicles and body armor with just a single round. All by myself.
5. Any bullet weight in 308 can cleanly kill any animal in North America. That might come in handy if I get hungry in a survival situation or if a bear in my 34 acre back yard gets hungry for me. A 55 grain 5.56 bullet may not be enough.
I could give you a few more reasons I like an AR-10, but that's my top 5.