Why have a .223 AK? Cuz I live in a house full of girls(Silly kashnikovians, .223 AKs are for chicks!). Since I already have a couple of ARs, getting an AK in 5.56 just makes sense, from all logistical angles. I know that gun buying rarely makes sense, but this works for me.
I only need to purchase and store one type of ammo for multiple weapons.
It is a fantastically light recoiling round, so I can have both the wife and the 13 year old daughter learning on Norinco 84s without fear of them being knocked around. This translates into enjoying time with me and learning some valuable skills and attitudes.
The underfolder is super compact and makes a great "get home" gun. I can "acquire" 5.56 way easier than 5.45 or 7.62x39 under a wider variety of circumstances. Does your local hardware store have .223? Your neighbor? That patrol car?
You can argue ballistics and accuracy all day, but if you want accuracy, than you should run screaming from AKs. If you want excellent terminal ballistics, you'd better learn what your cartridge is capable of long before you get into trouble. If you are really that concerned, there is a cartridge called 7.62 NATO that might be a better choice (I have heard rumors that this round is capable of accuracy, but you'd never know it by my shooting
).
For me, Ak is just a toy anyhow, if there was a SHTF, my 13 year-old would have it , while I hide behind another weapon system.