Eh.. that's norge..
The M4 isn't "less accurate" then a fullsize M16, it simply won't make such a big difference on lets say, 50 to 150 yards..
I'd prefer a M4 over an M16 anyday, it's more mobile, less weight to carry, and it can be stored much easier inside the vehicle..
An longer barrel makes a weapon more accurate, true.. but it only means fractions of MOA.. for a sharpshooter a reason to take the longer one, but an AR variant simply isn't ment to be a sniperrifle .. (maybe a designated marksman rifle.. but not more than that)
In stress situations an M4 is much nicer to have.. The length, weight and (your) foreward grip make it much more manouverable, thus making it more effective then a long M16. And in stress situations, that little bit of MOA is lost anyway, because your probably breathing like hell, scared shitless and in a uncomfortable shooting position.
The lighter weight also makes it easier to shoot in an upright position (standing), because your arms don't get tired that fast, and the weight balance is more to the back.
(And yes, I'm not military, but I shoot DSR (Dynamic Service Rifle) with a full length, uncompensated sabre defence XR41 (HK G3 clone..) topping the scales at 6,7 kg (incl. bipod, scope and 20rd .308 magazine) and shot a friends XR15 often (civil M4))
Sure, someone may one day kill me with my own gun.
But they'll have to beat me to death with it because it's empty.
A computer once beat me at chess, but it was no match for me at kick boxing.