Your rifle does not suck whether it is .223 or 5.56mm. But the mil chamber is more desirable on a field gun. The reasons are that they tend to be a tad more reliable (keep your gun clean and you should be ok anyway) and the 5.56 ammo tends to be more effective. The increased velocity and design of M193 bullets leads to some fragmentation of the round out to about 200 yards and many find this desirable. However, the .223 with slower velocities and perhaps a different style bullet, may not perform the same.
But if you just want this rifle for targets and plinking, the .223 is fine. It might even be a better choice because the tighter chamber usually results in better accuracy. If you want it for home defense, then just buy some Federal Premium Trophy Bonded 55 gr SP's. These tend to hold together very well allowing deep enough penetration with good expansion to be effective. Other good rounds for this are the 64 gr Winchester Power Point Plus and the Black Hills 60 gr SP. While these are expensive, you would only need a few boxes. Use cheap FMJ for everything else.