If you remember correctly the Italians were late comers to the war and only joined after receiving concessions from the French and English in terms of territory. So most of Italy was questioning the whole purpose behind going to war with Germany. Plus, along the Italian front the fighting was mostly in the Alps so it was a little harder on the troops. I mean imagine sitting in your little slice of Alp heaven hearing the Germans digging a tunnel above you that they were going to fill with TNT so that they could crush you to death. That would take a toll on any man.
Now compare that with the troop on the Western Front whose home land had been invaded and whose towns were being decimated. If it came down to it, I believe the French troops would have defended their country. The German's may have advanced further into France, but they were in no way prepared to make a determined break through. Plus, if the US and England saw that France was about to fall they would have thrown old men and boys into France to try and at least slow the Germans till a proper defense could be planned.
If you really think about it Germany breaking through the French lines could have allowed Britain to flank the German Army and cut them off from Greater Germany. Allowed enough time the French Army could form a defensive line on the other side of say Paris boxing in the German's a la Stalingrad. The American's could then have landed in Belgium and pushed into Germany taking Berlin with out much of a fight. That however would require an understanding of mobile warfare, something that the military leaders of this time did not have.
