I think Carbine has some really good points, however, I think there is another over-riding reason for pushing XM8:
The "Private Lynch Syndrome"
Bear with me on this.....
Most folks in the Army are support folks. Most of them touch a rifle once a year for annual qualification.
Annual qualification means less than 100 rds per person, on average? Yes no? (for the sake of argument, let's up the count to 250)
So....the vast majority of the US Army is firing less than 250 rds once per year. This is under safe, slow, and pristine range conditions.
Take these same folks, put them in a convoy (lost?) during a swirling sandstorm and hit them with small arms, RPG's, and light machineguns. What is the result?
A cluster-F@#% of mass proportions.....
.......Folks trying to fire/reload weapons they hardly touch, under stressful, combat conditions. You get all kinds of stoppages, mis-feeds, etc when this happens.
"my gun jammed...."
That's all you hear when support folks get hit.
Now...contrast this with the 3rd ID (Rock of the Marne...HOOAH!)
The USMC
The 101st Abn
and all of other frontline combat units that are at the tip of the spear.....
No major complaints about the M16/M4....Yes, there are niggling gripes about proper lube for a sandy envirionment and so forth, but no large scale tales of weapons going tits-up in a firefight either.
We know what the difference is:
Training, pure and simple......
There are those in the Army that want a "wonder gun" that any person (read: non-combat arms) can reliably use under most conditions......
A "wonder gun" that won't jam when used during a stressful event.....
A "wonder gun" that allows the Army to continue the trend of not giving support troops proper weapons training......
I personally feel that this is a major reason behind the XM8. It is not a weapon for the grunts, it is a weapon for the non-grunts.....